Remove unused code in test_validate.py

Remove the mock of instances.Instance.nova() for some tests.

Change-Id: I48aaaacaa827cd96ad2372011daf48e386e87c01
Don't use SSH in Rackspace::Cloud::Server

Rackspace Cloud Servers now supports config drive and the Rackspace
images have cloud-init installed by default, so we no longer have to SSH
to the Cloud Server to install dependencies and run the user-data
script.

Closes-Bug: #1298050
Change-Id: I5cb6a93c5b34b0a8cfe7480211da70d65638de54
Rackspace::Server::SSHWaitCondition resource

blueprint: ssh-wait-condition-resource
Change-Id: I566021b33809b6c6f606711b50ba48c5b67199c6