Add ability to switch database driver

Also added mysqlconnector packages into default installation.

blueprint enable-mysql-connector

Change-Id: Ib2cda7cb183dc8f0ff4759cc6e9ecab469fd121c
diff --git a/files/apts/keystone b/files/apts/keystone
index b7218b7..d316a42 100644
--- a/files/apts/keystone
+++ b/files/apts/keystone
@@ -6,6 +6,7 @@
 python-pysqlite2
 python-sqlalchemy
 python-mysqldb
+python-mysql.connector
 python-webob
 python-greenlet
 python-routes