database: fix PostgreSQL connection string

If all databases drivers are loaded, MySQL SQLAlchemy driver
overrides all the other one that might not have set one.
This patches fixes that.

Change-Id: If6d8d08e5b7b7c48ca012677b536d71058def6fd
Closes-Bug: #1493304

lib/database

@@ -101,7 +101,7 @@ 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=${BASE_SQL_CONN:-$(get_database_type)://$DATABASE_USER:$DATABASE_PASSWORD@$DATABASE_HOST}
+    BASE_SQL_CONN=${BASE_SQL_CONN:-$(get_database_type_$DATABASE_TYPE)://$DATABASE_USER:$DATABASE_PASSWORD@$DATABASE_HOST}
 
     return 0
 }
@@ -135,14 +135,6 @@ 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