oeqa.utils.git: introduce GitRepo.rev_parse()

(From OE-Core rev: 55726e931536ed0cbd7b80588060b05a3145c934)

Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/utils/git.py

@@ -38,5 +38,12 @@ class GitRepo(object):
             env.update(env_update)
         return self._run_git_cmd_at(git_args, self.top_dir, env=env)
 
+    def rev_parse(self, revision):
+        """Do git rev-parse"""
+        try:
+            return self.run_cmd(['rev-parse', revision])
+        except GitError:
+            # Revision does not exist
+            return None