mdmon: don't attempt to manage new arrays when terminating

mdmon: don't attempt to manage new arrays when terminating

When mdmon gets a SIGTERM, it stops managing arrays that are clean. If
there is more that one array in the container and one of them is dirty
and the clean one is still present in mdstat, mdmon will treat it as a
new array and start managing it again. This leads to a cycle of
remove_old() / manage_new() calls for the clean array, until the other
one also becomes clean.

Prevent this by not calling manage_new() if sigterm is set. Also, remove
a check for sigterm in manage_new() because the condition will never be
true.

Signed-off-by: Artur Paszkiewicz <artur.paszkiewicz@intel.com>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>