Add a new watcher option --ignore-pause

During cluster maintenance, when the watcher is disabled, it's useful to
run it just once. This is incovenient to do currently, as the watcher
needs to be unpaused, then run, then paused again.

This patch adds an option “--ignore-pause” that can be used to ignore
the cluster-level setting. Also the man page is updated as it was
missing the options available.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>