Fix for broken switch for config_drive

There's a wrong check in api.py, we should check if config_drive
is not a boolean string before we try to treat it as an image id

Fixes LP #1090148

Change-Id: I2e0bc49922781138e569471b0dd360fb3918b687

nova/compute/api.py

@@ -462,7 +462,7 @@ class API(base.Base):
 
             # Handle config_drive
             config_drive_id = None
-            if config_drive and config_drive is not True:
+            if config_drive and not utils.is_valid_boolstr(config_drive):
                 # config_drive is volume id
                 config_drive_id = config_drive
                 config_drive = None

nova/tests/api/openstack/compute/test_servers.py

@@ -2761,7 +2761,7 @@ class ServersControllerCreateTest(test.TestCase):
                     'open': 'stack',
                 },
                 'personality': {},
-                'config_drive': True,
+                'config_drive': "true",
             },
         }