src: Send out the output name for the remote role

src: Send out the output name for the remote role

A while ago we switched to activation-by-default turned off which passes
the responsability of activating applications to the shell client. The
shell client uses the app_id to indentify the application to display,
and the output.

The output would normally be hard-coded to the first available output
but there is nothing that prevents the shell to display it on other
outputs.

This patch does just that, it would allow the user use configurable
option in the ini file, under the [output], agl-shell-app-id=app_id, by
re-using the event from the compositor sent to the shell client to
pick up a different output, the one specified in the section entry.

Bug-AGL: SPEC-4529
Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
Change-Id: Ieea1a28fe6776ecc691fd38da9b4c3495ac5a5ea