Bug fixes, refactoring and "new" tests for the build manager

- Fixes various bugs introduced in the most recent build system commit
- Refactors state management in the build manager to be cleaner and more contained
- Adds back in the mock-based tests, fixed to not use threads and adjusted for the refactoring
- Adds some more simplified unit tests around non-etch related flows

buildman/jobutil/buildjob.py

@@ -57,10 +57,15 @@ class BuildJob(object):
   @lru_cache(maxsize=1)
   def _load_repo_build(self):
     try:
-      return model.build.get_repository_build(self.job_details['build_uuid'])
+      return model.build.get_repository_build(self.build_uuid)
     except model.InvalidRepositoryBuildException:
       raise BuildJobLoadException(
-          'Could not load repository build with ID %s' % self.job_details['build_uuid'])
+          'Could not load repository build with ID %s' % self.build_uuid)
+
+  @property
+  def build_uuid(self):
+    """ Returns the unique UUID for this build job. """
+    return self.job_details['build_uuid']
 
   @property
   def namespace(self):