Add disable all UST event(s) command

Note that you can only disable all events for a specific channel (like
the kernel). So, using the UST global domain (-u -a), only the event(s)
in the specified channel will be disabled for all registered
applications.

Bottom line, it disables all events in a channel.

Signed-off-by: David Goulet <david.goulet@polymtl.ca>