OPS-1593 As an operator, I want sudo_user converted to become user in roles and plays, for compatibility with Ansible 2.x

The headers were pointing to the old github wiki. Since we've officially
moved to Confluence, these links should be updated.

If a git version is specified as a branch, and the commit referred to is
already on the local working tree, but the branch is not, then the
checkout will fail.

This is because the Ansible 1.9.3 module would check to see if the
commit was already present, and if so, did not fetch. This meant the
branch wasn't defined in the local working tree.

This can happen if you make a branch but there aren't any changes on the
branch.

* Handles cert validation from behind a proxy better
* Also this commit updates build server validation (i.e. testcase
    paths) that have changed on platform

The test_build_server role was failing on acceptance tests because of unicode
static assets being gathered in collectstatic for django. This was because of
this issue https://github.com/ansible/ansible/issues/6655, which has been
resolved in recent ansible versions. We must override the version that is
being used by this repo, and upgrade ansible at provisioning time for
running the test_build_server role.

Also disables lettuce verification on test_build_server role.