mon: Guard injectargs parsing to prevent crashes on bad input
mon: Guard injectargs parsing to prevent crashes on bad input

While we're at it, reply to injectargs commands instead of
doing it silently.

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

ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph,ajnelson/ceph