build-unit-test-docker: use Gerrit revision if available

If Jenkins is triggering us to run CI on a package that is included
in the Docker image itself, use the requested revision-under-test as
part of the Docker image build process.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I61a0a249123800aba860ab1535e96f5cdb2ec63f
1 file changed