add-trigger: rename --fire-* to --rate-policy=*:value

add-trigger: rename --fire-* to --rate-policy=*:value

With the move to firing policy to the action and the renaming to rate
policy, a rename of the CLI options is necessary.

We introduce the following format:

  --rate-policy=<type>:<value>

Where type is either: once-after or every.
Value is an unsigned long long value.

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I6df264c536293e686033d0baa8fe870c75c28b8d