Switch to command pattern and using transaction chains

This patch does a few things:

1)  Switch to using command pattern with transaction chains
    to provider robust writing to the operational store
2)  Moved over the existing operational writing to using the command
    pattern
3)  Removed the bridges from the ovsdb node as they need to be
    separate topological nodes.

Change-Id: I9796d90a7cee483271134dc5abbc6097df4ce567
Signed-off-by: Ed Warnicke <eaw@cisco.com>