Rally needs bumping python-novaclient

python-novaclient <= 2.17 doesn't support authentification via
auth_token (at least without specifing username and password)

Which was changed here:
https://review.openstack.org/#/c/85920/

So it makes sense to bump version of novaclient

Change-Id: I6d2a0a414b89e757a48d6616c8e74ed34591d02b
Merge "Rally needs bumping python-novaclient"