add missing python-setuptools runtime dependency to debian/control

If missing ceph-deploy fails with a non trivial error message:

Traceback (most recent call last):
  File "/usr/bin/ceph-deploy", line 19, in <module>
    main()
  File "/usr/lib/python2.7/dist-packages/ceph_deploy/cli.py", line 83, in main
    args = parse_args(args=args, namespace=namespace)
  File "/usr/lib/python2.7/dist-packages/ceph_deploy/cli.py", line 53, in parse_args
    for ep in pkg_resources.iter_entry_points('ceph_deploy.cli')
  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 2012, in load
    if require: self.require(env, installer)
  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 2025, in require
    working_set.resolve(self.dist.requires(self.extras),env,installer))
  File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 594, in resolve
    raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: distribute