teuthology-nuke: identify and reboot machines with kernel mounts
teuthology-nuke: identify and reboot machines with kernel mounts

This includes untested code for just force-unmounting them
when that works again, but for now it does a full reboot-and-
reconnect cycle.

Signed-off-by: Greg Farnum <0bcb4295d38ee745130ea5f2bb88ef4eef474e61@dreamhost.com>

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