Include .terraform.lock.hcl in CopyTerraformFolderToDest

[Erouan50]

This commit adds in the filter from the function
CopyTerragruntFolderToDest an exclusion exception for the lock file.

The .terraform.lock.hcl used by Terraform to lock the versions of
the providers is not included during the copy. It can bring weird
behaviors when the copy is skipped (check the function
test_structure.CopyTerraformFolderToDest) where version 1.1 of a
provider would be used in the example folder but might be updated during
the terraform init due to the copy without the lock file. The lock
file should be included within the copy to keep the same providers'
versions.

Fix: #1116

I ran the test from the modules/files. Here is the output:

Test completed without error, however due to a limitation in GNU diff < 3.3.0, directories have not been compared for equivalency.
PASS
ok      github.com/gruntwork-io/terratest/modules/files 0.005s

I try to run the tests from the modules/terraform, but a lot of them fail
(they fail as well from master) and don't seem to be related to my changes.

[yorinasub17]

LGTM! Thanks for your contribution! I'll kick off a regression test and if it passes, will merge this in.

[yorinasub17]

Build failed, but for a known failure on master. I rebased your test branch and kicked off a new build here:

https://app.circleci.com/pipelines/github/gruntwork-io/terratest/988/workflows/1fef1dfe-f43d-4f3c-81c4-6cd68ee6d9d3

[yorinasub17]

The updated build failed, but for a known failure from master unrelated to this change, so we can merge this in! Thanks again for the contribution!

[Erouan50]

You're welcome, thank you!