Screwdriver: Git submodules are not up to date in PR builds

[jithine]

What happened:

SD builds for PRs do not update the submodule to its latest state specified in the PR branch, but instead uses the state specified in master branch (PR target branch). PR builds try to merge the branch with master, but submodules are not being updated.

What you expected to happen:

SD builds should respect the submodule state in the PR builds.

How to reproduce it:

1. Create a repo with a submodule, pointing to a commit (commit1).
2. Create a new branch, update the submodule to a new commit (commit2).
3. Create a PR.
4. SD will build the PR branch, but the submodule will be in the state of commit1, instead of commit2.

[marian-r]

@jithin1987 thanks for creating this 👍

[jithine]

This should be fixed now.