Fixed tenant_id and device_id filtering

Changes made after the network sharing busted tenant_id based filtering.
Also noticed that the model_query call was making an explicit filtering
choice on Ports for device_id, so that particular filter was moved into
the port_find method.
Merge pull request #167 from Cerberus98/master

Fixed tenant_id and device_id filtering.
Default net assignment

Adds default network assignment to Quark, along with yanking out
repoze.tm2 for compatibility while reinstating the standard
sqlalchemy-style transaction sessions to eliminate the race condition in
mass-assigning IP addresses under load.

Also fixes a typo with ipam_reuse_after which was previously, and
incorrectly, a boolean config value.
Merge pull request #168 from Cerberus98/transaction_merge

Default net assignment