Reconnect to Gerrit database if needed

* jeepyb/gerritdb.py(connect): If the database connection is being
reused for a connect call, issue a ping and pass the reconnect
option so that a reconnection attempt will be made in the event the
socket has timed out or otherwise disconnected. Note that this only
works for the MySQLdb driver, so a different solution will likely be
needed for psycopg2. Alternatively, switching to an ORM like
sqlalchemy would get us this for free, but is a more involved
change.

Change-Id: I591d40998e208f18ac5c43bafd7bccb98be6a9c8
Closes-Story: #2000017

jeepyb/gerritdb.py

@@ -60,4 +60,11 @@ def connect():
             import psycopg2
             db_connection = psycopg2.connect(
                 host=DB_HOST, user=DB_USER, password=DB_PASS, database=DB_DB)
+    else:
+        try:
+            # Make sure the database is responding and reconnect if not
+            db_connection.ping(True)
+        except AttributeError:
+            # This database driver lacks a ping implementation
+            pass
     return db_connection