support tags for dns and vpn resource

[ShiChangkuo]

the testing result as follows:

$ make testacc TEST='./huaweicloud' TESTARGS='-run TestAccDNSV2PtrRecord_basic'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./huaweicloud -v -run TestAccDNSV2PtrRecord_basic -timeout 360m
=== RUN   TestAccDNSV2PtrRecord_basic
--- PASS: TestAccDNSV2PtrRecord_basic (50.27s)
PASS
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud       50.303s

$ make testacc TEST='./huaweicloud' TESTARGS='-run TestAccDNSV2RecordSet_basic'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./huaweicloud -v -run TestAccDNSV2RecordSet_basic -timeout 360m
=== RUN   TestAccDNSV2RecordSet_basic
--- PASS: TestAccDNSV2RecordSet_basic (61.73s)
PASS
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud       61.781s

$ make testacc TEST='./huaweicloud' TESTARGS='-run TestAccVpnSiteConnectionV2_basic'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./huaweicloud -v -run TestAccVpnSiteConnectionV2_basic -timeout 360m
=== RUN   TestAccVpnSiteConnectionV2_basic
--- PASS: TestAccVpnSiteConnectionV2_basic (287.59s)
PASS
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud       287.648s