git_functions: propagate environment variables

[lexton]

Proposed solution for: #2085

[denis256]

👍
However failed multiple tests related to git invocation

TestGetRepoRoot
TestGetPathFromRepoRoot
TestGetPathToRepoRoot
TestShowWarningWithDependentModulesBeforeDestroy

time=2022-04-27T14:31:50Z level=debug msg=Running command: terraform --version prefix=[/home/circleci/project/test/fixture-include-multiple/expose/vpc] 
Releasing state lock. This may take a few moments...
=== CONT  TestGetRepoRoot
    integration_test.go:2791: 
        	Error Trace:	integration_test.go:2791
        	Error:      	Received unexpected error:
        	            	unexpected end of JSON input
        	Test:       	TestGetRepoRoot
--- FAIL: TestGetRepoRoot (152.85s)

Apply complete! Resources: 1 added, 0 changed, 0 destroyed.
...
Initializing provider plugins...
- Finding latest version of hashicorp/random...
--- PASS: TestAWSGetCallerIdentityFunctions (157.69s)
- Installing hashicorp/random v3.1.3...
=== CONT  TestGetPathFromRepoRoot
    integration_test.go:2824: 
        	Error Trace:	integration_test.go:2824
        	Error:      	Received unexpected error:
        	            	unexpected end of JSON input
        	Test:       	TestGetPathFromRepoRoot
--- FAIL: TestGetPathFromRepoRoot (158.33s)
...
You can apply this plan to save these new output values to the Terraform
state, without changing any real infrastructure.
=== CONT  TestGetPathToRepoRoot
    integration_test.go:2856: 
        	Error Trace:	integration_test.go:2856
        	Error:      	Received unexpected error:
        	            	unexpected end of JSON input
        	Test:       	TestGetPathToRepoRoot
--- FAIL: TestGetPathToRepoRoot (159.54s)
--- PASS: TestPreventDestroyOverride (159.63s)
...
=== RUN   TestShowWarningWithDependentModulesBeforeDestroy
    integration_test.go:3726: Copying fixture-destroy-warning to /tmp/terragrunt-test165306862
runTerragruntVersionCommand after split
[terragrunt run-all init --terragrunt-non-interactive --terragrunt-working-dir /tmp/terragrunt-test165306862/fixture-destroy-warning]
runTerragruntVersionCommand after split
[terragrunt run-all apply --terragrunt-non-interactive --terragrunt-working-dir /tmp/terragrunt-test165306862/fixture-destroy-warning]
runTerragruntVersionCommand after split
[terragrunt destroy --terragrunt-non-interactive --terragrunt-working-dir /tmp/terragrunt-test165306862/fixture-destroy-warning/vpc]
    integration_test.go:4340: 
        	Error Trace:	integration_test.go:4340
        	Error:      	Not equal: 
        	            	expected: 1
        	            	actual  : 0
        	Test:       	TestShowWarningWithDependentModulesBeforeDestroy
--- FAIL: TestShowWarningWithDependentModulesBeforeDestroy (6.73s)

I think it is related to setting opts.Writer = &stdout on options.TerragruntOptions which make git output to be passed to application output...

If issues occur only because of passed env variables, code can be extended to copy env variables:

	opts, _ := options.NewTerragruntOptions(path)
	opts.Env = terragruntOptions.Env