Close with statement earlier

This stuff doesn't need to be in the with statement
Use the with_statement from python3

http://legacy.python.org/dev/peps/pep-0343/

call __exit__ correctly from novaclient

https://github.com/openstack/python-novaclient/commit/98934d7bf1464afe0f7fe98efd2a591d95ac9c41#diff-709c13ba674c4ae39f66e0ff604c1c21R172