Bring over the rails gem cleanup from omnibus

Closes gitlab-org/distribution/team-tasks#520

See merge request gitlab-org/build/CNG!316

Ensure mailroom is updated when it's dockerfile changes

Closes gitlab-com/gl-infra/delivery#562

See merge request gitlab-org/build/CNG!319

Fixes an issue where mailroom wasn't taking into account the version of
it's project folder when determined whether a new build was needed.

This directory contains a unit test key that causing some scanning programs
to flag it

Remove unnecessary test data

So we don't need to prune here

Bump container registry to v2.7.6-gitlab

See merge request gitlab-org/build/CNG!317

Golang: update to 1.12.13

Closes gitlab-org/charts/gitlab#1569

See merge request gitlab-org/build/CNG!315

This matches the gem exclusions used in the GitLab Omnibus project

Closes https://gitlab.com/gitlab-org/charts/gitlab/issues/1569

Update the Go version to 1.12.13, latst of the 1.12 minors as of
2019-10-31

https://golang.org/doc/devel/release.html#go1.12.minor

Workaround for conflicting defaults in UBI repos

See merge request gitlab-org/build/CNG!314

rails: wait-for-deps output messages and doc reference

Closes gitlab-org/charts/gitlab#1062

See merge request gitlab-org/build/CNG!313

Add messaging to the `wait-for-deps` script, and reference to docs
when the container continues to restart due to issues with state of
data migrations / services.

Closes https://gitlab.com/gitlab-org/charts/gitlab/issues/1062

Mailroom: Remove the wrapper script

See merge request gitlab-org/build/CNG!309

* This fixes an issue where the ruby process would start, but if it were
to fail, we lose that context, and container would continue to run
despite the intent of this container no longer doing any work
* I'm not sure why the wrapper script or the creation of a log file are
necessary
* mail_room outputs to stdout by default
  * Our helm charts also do not configure the `log_path` option
  * due to this I elected to start the ruby process natively
  * output goes to stdout and if the process dies for any reason, so
  will the container

CI: Exit appropriately when docker image syncing fails

See merge request gitlab-org/build/CNG!305

Gitaly: Add internal_socket_dir

See merge request gitlab-org/build/CNG!303

Pre-create shared tmp for Rails in unicorn/workhorse

See merge request gitlab-org/build/CNG!308

Rails likes a tmpdir permissions set _just so_. To ensure everything is
happy (as seen in gitlab-org/charts/gitlab#1651), pre-create this if it
does not already exist, and set the permissions to match the expectation
of Rails (not a Ruby-ism)

Bump container registry to v2.7.5-gitlab

See merge request gitlab-org/build/CNG!307

This brings in a single logging change to track down 0-byte uploads:
https://gitlab.com/gitlab-org/container-registry/merge_requests/8

Signed-off-by: Balasankar "Balu" C <balasankar@gitlab.com>

rails: match the revision format from omnibus

See merge request gitlab-org/build/CNG!304