[#115624569] Workaround terraform codecommit issue with default_branch property

[keymon]

#115624569 Implement locking for pipelines

What?

We did not catch this issue in the PR #173.

Terraform codecommit resource[1] has a bug managing the default_branch
property: hashicorp/terraform#5641

Although this property is optional, terraform will try to manage it.

If defined, codecommit will fail during creation:

BranchDoesNotExistException: refs/heads/master does not exist

Meanwhile if default_branch is defined, codecommit it will fail as soon
as a branch is pushed to the repository. The reason is that AWS enforces
having at least one branch as default branch, failing when terraform is
trying to set it empty:

  * aws_codecommit_repository.concourse-pool: Error Updating Default
  * Branch for CodeCommit Repository: InvalidParameter: 1 validation
    * errors:
     - field too short, minimum length 1: DefaultBranchName

Scope

This issue will be reported upstream, but meanwhile we will workaround it by
passing the default branch as a variable, and quering it using awscli.
If the respository does not exist or does not have default branch, the
variable will be set to empty string "".

We additionally remove the bump of the pipeline-trigger in the init job, which is not required anymore.

How to test

Running from a environment without an associated codecommit git pool-resource
respository:

1. Run the bootstrap process SELF_UPDATE_PIPELINE=false BRANCH=$(git rev-parse --abbrev-ref HEAD) make dev bootstrap DEPLOY_ENV=...
2. Run the jobs up to concourse-terraform (the rest are not relevant)
   • concourse-terraform should finnish OK
   • the terraform apply output for the resource aws_codecommit_repository.concourse-pool should not refer to any default_branch
3. Rerun concourse-terraform it should end OK.
4. Run the lock-pipeline job in create-bosh-cloudfoundry
   a. Upload the pipelines: SELF_UPDATE_PIPELINE=false BRANCH=$(git rev-parse --abbrev-ref HEAD) make dev pipelines DEPLOY_ENV=...
   b. This will create a initial branch in the codecommit repo.
5. Back in the bootstrap concourse (http://localhost:8080), rerun concourse-terraform
   • It should finish OK
   • terraform output should not report any change

Who?

Anyone but @keymon

[dcarley]

Haven't tested, but this look reasonable given the circumstances 👌

[keymon]

I did a PR on terraform to fix the issue, although I am not sure if this is the right way to implement it: hashicorp/terraform#5904

One alternative can be just use the patched version and bundle it in the terraform container, but it that case we will have a dependency on that branch.

[mtekel]

works well, merging