Fix: send disable ALL command code if event is *

$ lttng disable-event -a
and
$ lttng disable-event '*'

Both commands should do the same meaning send the DISABLE_EVENT_ALL
command to the session daemon.

Signed-off-by: David Goulet <dgoulet@efficios.com>
Fix: disable-event for an agent domain

This fixes the disable-event command for an agent that was not working
properly in the case an application was spawned after the command.

Also, for the disable all event command for an agent, the disable
command will try first to disable the '*' event and will disable all
already existing events after. This is to make sure the refcount on the
agent side is synchronized with the amount of enable event prior.

Fixes #831

Signed-off-by: David Goulet <dgoulet@efficios.com>
Test: add disable-event JUL tests

Signed-off-by: David Goulet <dgoulet@efficios.com>