Add ability to switch database driver

Also added mysqlconnector packages into default installation.

blueprint enable-mysql-connector

Change-Id: Ib2cda7cb183dc8f0ff4759cc6e9ecab469fd121c

lib/database

@@ -89,7 +89,7 @@ function initialize_database_backends {
     # a multi-node DevStack installation.
 
     # NOTE: Don't specify ``/db`` in this string so we can use it for multiple services
-    BASE_SQL_CONN=${BASE_SQL_CONN:-${DATABASE_TYPE}://$DATABASE_USER:$DATABASE_PASSWORD@$DATABASE_HOST}
+    BASE_SQL_CONN=${BASE_SQL_CONN:-$(get_database_type)://$DATABASE_USER:$DATABASE_PASSWORD@$DATABASE_HOST}
 
     return 0
 }
@@ -120,6 +120,14 @@ function database_connection_url {
     database_connection_url_$DATABASE_TYPE $db
 }
 
+function get_database_type {
+    if [[ -n "${SQLALCHEMY_DATABASE_DRIVER}" ]]; then
+        echo "${DATABASE_TYPE}+${SQLALCHEMY_DATABASE_DRIVER}"
+    else
+        echo "${DATABASE_TYPE}"
+    fi
+}
+
 
 # Restore xtrace
 $XTRACE