Follow changes in Nova trunk

Trunk changed the structure of tests directory by introducing
a new unit package:
Id42ba373c1bda6a312b673ab2b489ca56da8c628

Instance Info is now an object as well, not a dicitionary:
Ia4e4639ec1a593380b48f8f6e4962dd22ab8fc0b

instance_type parameter has been added to spawn:
Ieebfcbc2478ba8d7036c1af30efbbf640aa7df73

Change-Id: I06a2d02e65cd3eb0813caf3972013500d94d493c