crtools: kill all dumped processes by default

If a process continue to run, it may change a state of filesystem.

@gorcunov:
 - Drop -k option, it's not needed anymore.
 - Allow -c option (continue execution of a
   process after being dumped) in dumping procedure.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>