Check description of machines before nuking when -a is passed

When teuthology-nuke is passed with --archive/-a to kill and nuke machines
from an archive folder it blindly will nuke all the targets it grabs from the
config.yaml in the archive dir. This change will check the description of
locked machines and make sure the run name is in the description. if not it
removes the target from the list passed to nuke().

Signed-off-by: Sandon Van Ness <sandon@inktank.com>