Fail faster when docker isn't running

In order to make build.py more friendly, have it fail faster
when the script is unable to connect to Docker because it's not
running.

Change-Id: I6d480e601ea2511df9396fcf4e89c06c06d4c21c
Closes-Bug: #1488133

kolla/cmd/build.py

@@ -32,6 +32,7 @@ import time
 
 import docker
 import jinja2
+from requests.exceptions import ConnectionError
 
 logging.basicConfig()
 LOG = logging.getLogger(__name__)
@@ -68,6 +69,13 @@ class WorkerThread(Thread):
                 self.queue.task_done()
             except Queue.Empty:
                 break
+            except ConnectionError as e:
+                LOG.error(e)
+                LOG.error('Make sure Docker is running and that you have '
+                          'the correct privileges to run Docker (root)')
+                data['status'] = "connection_error"
+                self.queue.task_done()
+                break
 
     def process_source(self, source, dest_dir):
         if source.get('type') == 'url':
@@ -89,7 +97,10 @@ class WorkerThread(Thread):
         image['status'] = "building"
 
         if image['parent'] is not None and \
-           image['parent']['status'] in ['error', 'parent_error']:
+           image['parent']['status'] in ['error', 'parent_error',
+                                         'connection_error']:
+            LOG.error('Parent image error\'d with message "%s"',
+                      image['parent']['status'])
             image['status'] = "parent_error"
             return