Remote: add init_system property
Remote: add init_system property

So far, this only exists to answer the question: "does this host use
systemd?" - in which case it will return 'systemd'. Else it will return
None.

Signed-off-by: Zack Cerza <d7cdf09fc0f0426e98c9978ee42da5d61fa54986@redhat.com>

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