nuke: Reimage instead of nuking as necessary
nuke: Reimage instead of nuking as necessary

Once this branch is in master, we'll probably want to switch this
behavior to no-op nodes that would be reimaged, since the next job will
do that anyway.

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

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