Refactoring: Merge TryJob and Build class and move Build class to buildbot module.

Before this patch, there is a Build class in rebaseline.py (added in http://crrev.com/2164153002) and a TryJob class in rietveld.py, which serve the same function. This CL merges them together and moves them to another location.

Review-Url: https://codereview.chromium.org/2181533002
Cr-Commit-Position: refs/heads/master@{#407877}
4 files changed