add combined method for creating databases with users

- implement userdbs.models.UserDatabaseManager.create_userdatabase_with_user to
  setup a new database with a new database user in one step

gnuviechadmin/userdbs/models.py

@@ -202,6 +202,26 @@ class UserDatabaseManager(models.Manager):
                 break
         return nextname
 
+    @transaction.atomic
+    def create_userdatabase_with_user(
+        self, db_type, osuser, password=None, commit=True):
+        """
+        Creates a new user database with a new user.
+
+        :param db_type: database type from :py:data:`DB_TYPES`
+        :param osuser: :py:class:`osusers.models.OsUser` instance
+        :param str password: the password of the new database user
+        :param boolean commit: whether the user and the database should be
+            persisted
+        :return: database instance
+        :rtype: :py:class:`UserDatabase`
+
+        """
+        dbuser = DatabaseUser.objects.create_database_user(
+            osuser, db_type, password=password, commit=commit)
+        database = self.create_userdatabase(dbuser, commit=commit)
+        return database
+
     @transaction.atomic
     def create_userdatabase(self, db_user, db_name=None, commit=True):
         """