Volume namespaces - fixes 771

Fixes #771.

Some temporary code is in place so this doesn't break the rest of the system.
See below:

```
 except ValueError:
-                    # If we can't split on `.` and get two parts then it's not
-                    # a filesystem Flocker is managing.  Likewise if we can't
-                    # interpret the bit before the `.` as a UUID.  Perhaps a
-                    # user created it, who knows.  Just ignore it.
+                    # If we can't split on `.` and get three parts then
+                    # it's not a filesystem Flocker is managing.  Likewise
+                    # if we can't interpret the bit before the `.` as a
+                    # UUID.  Perhaps a user created it, who knows.  Just
+                    # ignore it.
                     continue
```