Implement NeutronPollingMinion

Add NeutronPollingMinion as a minion of the cluster daemon. Also fixes
some bugs with Neutron deserialization. With this change, we can poll
Neutron for tasks and translate them into high-level (Neutron)
protobuf messages, but fail in translation due to lack of implemented
translators (Coming Soon!)

Signed-off-by: Brandon Berg <bberg@midokura.com>
Change-Id: I73716dd2ff2335b3604b671683aa0b6dad550cc8