repo-pull: Check Gerrit Code Review domain name

This commit adds a search on Gerrit Code Review URL so that a better
error message can be shown to users and the setup instructions can be
presented.

Test: repo_pull.py json -g [gerrit] [query]
Test: repo_review.py -g [gerrit] [query] -l Code-Review 2
Change-Id: I1f819c51e34c573f526ca3e30e237cdaf8a27160