Return database connection string validation

It was decided to keep validation for database connection
string in modules, because some components don't support
all backends (sqlite, mysql, pymysql, postgresql and mongodb).
E.g. nova doesn't use mongodb, that's why validation is needed.

Change-Id: I7999a0524e8b7346cc6873f4d45fff7e5be8edf7

manifests/db.pp

@@ -93,6 +93,9 @@ class nova::db (
 
   if !is_service_default($database_connection_real) {
 
+    validate_re($database_connection_real,
+      '^(sqlite|mysql(\+pymysql)?|postgresql):\/\/(\S+:\S+@\S+\/\S+)?')
+
     oslo::db { 'nova_config':
       connection       => $database_connection_real,
       idle_timeout     => $database_idle_timeout_real,