Added pre-transfer check for OSP volume, waiting for 'available'

Added a check before the OSP volume transfer begins, so that
we do not attempt to move the volume before it it is possible.
OSP volume has to be in the 'available' state before the transfer
begins. We are looping through TIMEOUT seconds (currently 300)
before giving up and erroring out.

wrapper/hosts.py

@@ -364,9 +364,34 @@ def handle_finish(self, data, state):
                           state['internal']['disk_ids'])
             logging.debug('Assumed volume list: %r', volumes)
             return False
-        # Move volumes to destination project
         for vol in volumes:
-            logging.info('Transfering volume: %s', vol)
+            logging.info('Transferring volume: %s', vol)
+            # Checking if volume is in available state
+            is_available = False
+            start_at = time.time()
+            while start_at + TIMEOUT > time.time():
+                volume_state = self._run_openstack([
+                        'volume', 'show', '-f', 'value', '-c', 'status', vol,
+                        ], data)
+                if volume_state is None:
+                    error('Unable to get volume state, quitting.')
+                    return False
+                volume_state = volume_state.rstrip()
+                logging.info('Current volume state: %s.', volume_state)
+                if volume_state == 'available':
+                    logging.info(
+                        'Volume detached in %s second(s), trasferring.',
+                        int(time.time() - start_at))
+                    is_available = True
+                    break
+                time.sleep(20)
+            if not is_available:
+                error(
+                    'Volume did not get ready (available) '
+                    'for transfer within %s seconds.',
+                    TIMEOUT)
+                return False
+            # Move volumes to the destination project
             transfer = self._run_openstack([
                 'volume', 'transfer', 'request', 'create',
                 '--format', 'json',