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

lib/databases/mysql

@@ -12,12 +12,6 @@ MY_XTRACE=$(set +o | grep xtrace)
 set +o xtrace
 
 MYSQL_DRIVER=${MYSQL_DRIVER:-PyMySQL}
-# Force over to pymysql driver by default if we are using it.
-if is_service_enabled mysql; then
-    if [[ "$MYSQL_DRIVER" == "PyMySQL" ]]; then
-        SQLALCHEMY_DATABASE_DRIVER=${SQLALCHEMY_DATABASE_DRIVER:-"pymysql"}
-    fi
-fi
 
 register_database mysql
 
@@ -30,6 +24,14 @@ fi
 # Functions
 # ---------
 
+function get_database_type_mysql {
+    if [[ "$MYSQL_DRIVER" == "PyMySQL" ]]; then
+        echo mysql+pymysql
+    else
+        echo mysql
+    fi
+}
+
 # Get rid of everything enough to cleanly change database backends
 function cleanup_database_mysql {
     stop_service $MYSQL

lib/databases/postgresql

@@ -21,6 +21,10 @@ register_database postgresql
 # Functions
 # ---------
 
+function get_database_type_postgresql {
+    echo postgresql
+}
+
 # Get rid of everything enough to cleanly change database backends
 function cleanup_database_postgresql {
     stop_service postgresql