ceph-deploy: support overrides
ceph-deploy: support overrides

Something like

overrides:
  ceph-deploy:
    foo: bar

Signed-off-by: Sage Weil <6dd34506bbd5e58221bbb3e4732d97c91f02277b@inktank.com>

ceph/teuthology,dmick/teuthology,SUSE/teuthology,caibo2014/teuthology,tchaikov/teuthology,SUSE/teuthology,dreamhost/teuthology,tchaikov/teuthology,yghannam/teuthology,ivotron/teuthology,michaelsevilla/teuthology,robbat2/teuthology,ivotron/teuthology,zhouyuan/teuthology,zhouyuan/teuthology,ktdreyer/teuthology,caibo2014/teuthology,ceph/teuthology,ktdreyer/teuthology,SUSE/teuthology,t-miyamae/teuthology,dmick/teuthology,t-miyamae/teuthology,michaelsevilla/teuthology,dreamhost/teuthology,yghannam/teuthology,dmick/teuthology,robbat2/teuthology