sql: add buildset.branch column

This change adds the build's branch information to the database.

Change-Id: Ia1e234f556766cc945dec84759c6a31f244084f6
diff --git a/tests/unit/test_connection.py b/tests/unit/test_connection.py
index c45da94..bacdf8f 100644
--- a/tests/unit/test_connection.py
+++ b/tests/unit/test_connection.py
@@ -74,7 +74,7 @@
         buildset_table = table_prefix + 'zuul_buildset'
         build_table = table_prefix + 'zuul_build'
 
-        self.assertEqual(13, len(insp.get_columns(buildset_table)))
+        self.assertEqual(14, len(insp.get_columns(buildset_table)))
         self.assertEqual(10, len(insp.get_columns(build_table)))
 
     def test_sql_results(self):
@@ -139,6 +139,7 @@
                 uuid=buildset0_builds[0]['uuid']),
             buildset0_builds[0]['log_url'])
         self.assertEqual('check', buildset1['pipeline'])
+        self.assertEqual('master', buildset1['branch'])
         self.assertEqual('org/project', buildset1['project'])
         self.assertEqual(2, buildset1['change'])
         self.assertEqual('1', buildset1['patchset'])