Make down idempotent, continue to remove resources if one is missing.

Signed-off-by: Daniel Nephin <dnephin@docker.com>

compose/network.py

@@ -149,7 +149,10 @@ class ProjectNetworks(object):
         if not self.use_networking:
             return
         for network in self.networks.values():
-            network.remove()
+            try:
+                network.remove()
+            except NotFound:
+                log.warn("Network %s not found.", network.full_name)
 
     def initialize(self):
         if not self.use_networking:

compose/volume.py

@@ -76,7 +76,10 @@ class ProjectVolumes(object):
 
     def remove(self):
         for volume in self.volumes.values():
-            volume.remove()
+            try:
+                volume.remove()
+            except NotFound:
+                log.warn("Volume %s not found.", volume.full_name)
 
     def initialize(self):
         try: