Allow parallel running of DX VIF acceptance tests

[ewbankkit]

Fixes #6244.
Acceptance tests:

$ DX_CONNECTION_ID=dxcon-xxxxxxxx AWS_DEFAULT_REGION=us-east-1 make testacc TESTARGS='-run=TestAccAwsDxPrivateVirtualInterface_'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./... -v -parallel 20 -run=TestAccAwsDxPrivateVirtualInterface_ -timeout 120m
?   	github.com/terraform-providers/terraform-provider-aws	[no test files]
=== RUN   TestAccAwsDxPrivateVirtualInterface_basic
=== PAUSE TestAccAwsDxPrivateVirtualInterface_basic
=== RUN   TestAccAwsDxPrivateVirtualInterface_dxGateway
=== PAUSE TestAccAwsDxPrivateVirtualInterface_dxGateway
=== RUN   TestAccAwsDxPrivateVirtualInterface_mtuUpdate
=== PAUSE TestAccAwsDxPrivateVirtualInterface_mtuUpdate
=== CONT  TestAccAwsDxPrivateVirtualInterface_basic
=== CONT  TestAccAwsDxPrivateVirtualInterface_mtuUpdate
=== CONT  TestAccAwsDxPrivateVirtualInterface_dxGateway
--- PASS: TestAccAwsDxPrivateVirtualInterface_basic (514.47s)
--- PASS: TestAccAwsDxPrivateVirtualInterface_dxGateway (525.06s)
--- PASS: TestAccAwsDxPrivateVirtualInterface_mtuUpdate (1181.31s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	1182.206s

$ DX_CONNECTION_ID=dxcon-xxxxxxxx AWS_DEFAULT_REGION=us-east-1 make testacc TESTARGS='-run=TestAccAwsDxPublicVirtualInterface_'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./... -v -parallel 20 -run=TestAccAwsDxPublicVirtualInterface_ -timeout 120m
?   	github.com/terraform-providers/terraform-provider-aws	[no test files]
=== RUN   TestAccAwsDxPublicVirtualInterface_basic
=== PAUSE TestAccAwsDxPublicVirtualInterface_basic
=== CONT  TestAccAwsDxPublicVirtualInterface_basic
--- PASS: TestAccAwsDxPublicVirtualInterface_basic (45.12s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	45.975s

$ DX_HOSTED_VIF_OWNER_ACCOUNT=000000000000 DX_CONNECTION_ID=dxcon-xxxxxxxx AWS_DEFAULT_REGION=us-east-1 make testacc TESTARGS='-run=TestAccAwsDxHostedPrivateVirtualInterface_'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./... -v -parallel 20 -run=TestAccAwsDxHostedPrivateVirtualInterface_ -timeout 120m
?   	github.com/terraform-providers/terraform-provider-aws	[no test files]
=== RUN   TestAccAwsDxHostedPrivateVirtualInterface_basic
=== PAUSE TestAccAwsDxHostedPrivateVirtualInterface_basic
=== RUN   TestAccAwsDxHostedPrivateVirtualInterface_mtuUpdate
=== PAUSE TestAccAwsDxHostedPrivateVirtualInterface_mtuUpdate
=== CONT  TestAccAwsDxHostedPrivateVirtualInterface_basic
=== CONT  TestAccAwsDxHostedPrivateVirtualInterface_mtuUpdate
--- PASS: TestAccAwsDxHostedPrivateVirtualInterface_basic (32.75s)
--- PASS: TestAccAwsDxHostedPrivateVirtualInterface_mtuUpdate (89.55s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	90.375s

$ DX_HOSTED_VIF_OWNER_ACCOUNT=000000000000 DX_CONNECTION_ID=dxcon-xxxxxxxx AWS_DEFAULT_REGION=us-east-1 make testacc TESTARGS='-run=TestAccAwsDxHostedPublicVirtualInterface_'
TF_ACC=1 go test ./... -v -parallel 20 -run=TestAccAwsDxHostedPublicVirtualInterface_ -timeout 120m
?   	github.com/terraform-providers/terraform-provider-aws	[no test files]
=== RUN   TestAccAwsDxHostedPublicVirtualInterface_basic
=== PAUSE TestAccAwsDxHostedPublicVirtualInterface_basic
=== CONT  TestAccAwsDxHostedPublicVirtualInterface_basic
--- PASS: TestAccAwsDxHostedPublicVirtualInterface_basic (35.30s)
PASS
ok  	github.com/terraform-providers/terraform-provider-aws/aws	36.147s

[bflad]

Looks great, @ewbankkit, thanks! 🚀

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!