Add DNS alias support

[matt-FFFFFF]

• Upgrade Azure DNS SDK to 2018-05-01
• Add support for aliases via TargetResource, as per https://godoc.org/github.com/Azure/azure-sdk-for-go/services/dns/mgmt/2018-05-01/dns#RecordSetProperties

Resources updated (including tests):

• azurerm_dns_a_record
• azurerm_dns_aaaa_record
• azurerm_dns_cname_record

The other recordset types do not support aliases.

Other progress

• docs

usage

resource "azurerm_dns_a_record" "alias" {
  name = "@"
  zone_name = azurerm_dns_zone.zone.name
  resource_group_name = azurerm_resource_group.rg.name
  ttl = 300

  /* Use the resource ID for a supported Azure resource here */
  target_resource_id = azurerm_frontdoor.site.id
} 

[matt-FFFFFF]

Acceptance tests for A records

 matt@DESKTOP-GCVSNIQ  ~/go/src/github.com/matt-FFFFFF/terraform-provider-azurerm   dnsalias  make testacc TESTARGS='-run=TestAccAzureRMDnsARecord'
==> Checking that code complies with gofmt requirements...
==> Checking that Custom Timeouts are used...
TF_ACC=1 go test $(go list ./... |grep -v 'vendor'|grep -v 'examples') -v -run=TestAccAzureRMDnsARecord -timeout 180m -ldflags="-X=github.com/terraform-providers/terraform-provider-azurerm/version.ProviderVersion=acc"
?       github.com/terraform-providers/terraform-provider-azurerm       [no test files]
=== RUN   TestAccAzureRMDnsARecord_basic
=== PAUSE TestAccAzureRMDnsARecord_basic
=== RUN   TestAccAzureRMDnsARecord_requiresImport
--- SKIP: TestAccAzureRMDnsARecord_requiresImport (0.00s)
    resource_arm_dns_a_record_test.go:43: Skipping since resources aren't required to be imported
=== RUN   TestAccAzureRMDnsARecord_updateRecords
=== PAUSE TestAccAzureRMDnsARecord_updateRecords
=== RUN   TestAccAzureRMDnsARecord_withTags
=== PAUSE TestAccAzureRMDnsARecord_withTags
=== RUN   TestAccAzureRMDnsARecord_withAlias
=== PAUSE TestAccAzureRMDnsARecord_withAlias
=== CONT  TestAccAzureRMDnsARecord_basic
=== CONT  TestAccAzureRMDnsARecord_withAlias
=== CONT  TestAccAzureRMDnsARecord_withTags
=== CONT  TestAccAzureRMDnsARecord_updateRecords
--- PASS: TestAccAzureRMDnsARecord_basic (82.44s)
--- PASS: TestAccAzureRMDnsARecord_updateRecords (99.21s)
--- PASS: TestAccAzureRMDnsARecord_withTags (101.57s)
--- PASS: TestAccAzureRMDnsARecord_withAlias (111.89s)
PASS

[matt-FFFFFF]

Acceptance tests for AAAA records

✘ matt@DESKTOP-GCVSNIQ  ~/go/src/github.com/matt-FFFFFF/terraform-provider-azurerm   dnsalias  make testacc TESTARGS='-run=TestAccAzureRMDnsAAAARecord'
==> Checking that code complies with gofmt requirements...
==> Checking that Custom Timeouts are used...
TF_ACC=1 go test $(go list ./... |grep -v 'vendor'|grep -v 'examples') -v -run=TestAccAzureRMDnsAAAARecord -timeout 180m -ldflags="-X=github.com/terraform-providers/terraform-provider-azurerm/version.ProviderVersion=acc"
?       github.com/terraform-providers/terraform-provider-azurerm       [no test files]
=== RUN   TestAccAzureRMDnsAAAARecord_basic
=== PAUSE TestAccAzureRMDnsAAAARecord_basic
=== RUN   TestAccAzureRMDnsAAAARecord_requiresImport
--- SKIP: TestAccAzureRMDnsAAAARecord_requiresImport (0.00s)
   resource_arm_dns_aaaa_record_test.go:43: Skipping since resources aren't required to be imported
=== RUN   TestAccAzureRMDnsAAAARecord_updateRecords
=== PAUSE TestAccAzureRMDnsAAAARecord_updateRecords
=== RUN   TestAccAzureRMDnsAAAARecord_withTags
=== PAUSE TestAccAzureRMDnsAAAARecord_withTags
=== RUN   TestAccAzureRMDnsAAAARecord_withAlias
=== PAUSE TestAccAzureRMDnsAAAARecord_withAlias
=== CONT  TestAccAzureRMDnsAAAARecord_basic
=== CONT  TestAccAzureRMDnsAAAARecord_withAlias
=== CONT  TestAccAzureRMDnsAAAARecord_withTags
=== CONT  TestAccAzureRMDnsAAAARecord_updateRecords
--- PASS: TestAccAzureRMDnsAAAARecord_basic (88.04s)
--- PASS: TestAccAzureRMDnsAAAARecord_withTags (102.99s)
--- PASS: TestAccAzureRMDnsAAAARecord_updateRecords (107.33s)
--- PASS: TestAccAzureRMDnsAAAARecord_withAlias (115.62s)
PASS

[matt-FFFFFF]

Acceptance tests for CNAME records

 ✘ matt@DESKTOP-GCVSNIQ  ~/go/src/github.com/matt-FFFFFF/terraform-provider-azurerm   dnsalias ●  make testacc TESTARGS='-run=TestAccAzureRMDnsCNameRecord'
==> Checking that code complies with gofmt requirements...
==> Checking that Custom Timeouts are used...
TF_ACC=1 go test $(go list ./... |grep -v 'vendor'|grep -v 'examples') -v -run=TestAccAzureRMDnsCNameRecord -timeout 180m -ldflags="-X=github.com/terraform-providers/terraform-provider-azurerm/version.ProviderVersion=acc"
?       github.com/terraform-providers/terraform-provider-azurerm       [no test files]
=== RUN   TestAccAzureRMDnsCNameRecord_basic
=== PAUSE TestAccAzureRMDnsCNameRecord_basic
=== RUN   TestAccAzureRMDnsCNameRecord_requiresImport
--- SKIP: TestAccAzureRMDnsCNameRecord_requiresImport (0.00s)
    resource_arm_dns_cname_record_test.go:43: Skipping since resources aren't required to be imported
=== RUN   TestAccAzureRMDnsCNameRecord_subdomain
=== PAUSE TestAccAzureRMDnsCNameRecord_subdomain
=== RUN   TestAccAzureRMDnsCNameRecord_updateRecords
=== PAUSE TestAccAzureRMDnsCNameRecord_updateRecords
=== RUN   TestAccAzureRMDnsCNameRecord_withTags
=== PAUSE TestAccAzureRMDnsCNameRecord_withTags
=== RUN   TestAccAzureRMDnsCNameRecord_withAlias
=== PAUSE TestAccAzureRMDnsCNameRecord_withAlias
=== CONT  TestAccAzureRMDnsCNameRecord_basic
=== CONT  TestAccAzureRMDnsCNameRecord_withTags
=== CONT  TestAccAzureRMDnsCNameRecord_updateRecords
=== CONT  TestAccAzureRMDnsCNameRecord_withAlias
--- PASS: TestAccAzureRMDnsCNameRecord_basic (83.34s)
=== CONT  TestAccAzureRMDnsCNameRecord_subdomain
--- PASS: TestAccAzureRMDnsCNameRecord_updateRecords (99.69s)
--- PASS: TestAccAzureRMDnsCNameRecord_withTags (104.40s)
--- PASS: TestAccAzureRMDnsCNameRecord_withAlias (108.71s)
--- PASS: TestAccAzureRMDnsCNameRecord_subdomain (79.74s)
PASS

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