Move firing policy from lttng_trigger to lttng_action

Move firing policy from lttng_trigger to lttng_action

After some reflection on the future of the importance of the trigger
feature and the centralization we wish to carry around it, it is
required that the notion of firing policy be moved from the trigger
object to each action object of a trigger.

This is necessary since we plan on introducing tracer side actions, such
as increment value of map. Controlling the firing policy on the tracer
side is not an easy thing to do since for UST tracing a lot a
synchronizations must take place and also we must define the behaviour
when multiple apps are present. Hence, we need a way to ensure that we
are not painting ourself in a corner. The middle ground that was chosen
was to move the notion of firing policy to the action object level. This
allows us to scope the concept to the action and decide for each type if
firing policy can be supported and, as needed, define the behaviour per
action type.

Essentially this patch perform the complete transition. It removes the
notion of firing policy at the trigger level and exposes the firing
policy of each action type if applicable.

CLI
======

For the `add-trigger` command the change essentially boils down to
moving the `--fire-every` and `--fire-once-after` from a top-level
parsing to the parsing of each actions. Yes, for now all actions
supports the `--fire-*` options but it will not be the case in the
future. A side effect of this is that a user could decide to have
different firing policy for each actions, but this also mean that if a
user want to apply the same firing policy across actions, the user needs
to specify it for each actions. This could be solved in the future as
the trigger feature matures and that common ground are found in the
behaviour or implementation of the actions (tracer side action, async
action, sync actions etc.) such that "syntactic sugar" options emerge.

As for the `list-trigger`, we move the firing policy printing to each
actions.

Tests have been updated to reflect the changes.

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: Ib29d4319922096c0c4b3f00782f3bbefb17e2f40