haas.model.Switch: Changed the name of the `model` column to `driver`

This is a more accurate description and doesn't collide with the term
"database model," which makes it less confusing.
Added some tests for switch_{register,delete}

These are failing, since the functions have not yet been implemented.
Implemented `switch_register`.

This fixes two of the test failures from the last commit.
switch_delete

Fixes the other two test failures.
switch_{register,delete}: implemented http/cli wrappers.
Add API calls for dealing with ports
Merge remote-tracking branch 'remotes/zenhack/switch_register/delete' into switch_register/delete

Conflicts:
	haas/api.py
Implement port_{register,delete}

There are large number of error conditions that are not checked for---for
instance, having a port_label that is not an integer.
Merge branch 'switch_register/delete' into connect_network
Implement port_{connect,detach}_nic