orchestra/remote.py: raise if ensure_online() fails
orchestra/remote.py: raise if ensure_online() fails

to ensure that we fail early if we cannot ensure an online remote.

Signed-off-by: Kefu Chai <a4b264ee037c625052534d60505bfd0db4776ac4@redhat.com>

dmick/teuthology,ceph/teuthology,ktdreyer/teuthology,SUSE/teuthology,dmick/teuthology,dmick/teuthology,SUSE/teuthology,ktdreyer/teuthology,ceph/teuthology,SUSE/teuthology