shell: Not not override the agl_shell interface resources

shell: Not not override the agl_shell interface resources

This redoes a bit the way we assigned wl_resources created in case we got
a bound_ok or bound_fail event.

Previously, even if we get a 'bound_fail' event we would override the
shell_client.resource which would make activation of the legitimate
shell client impossible, so this change would make the shell_client.resource
not being set if that happens.

Secondly, this includes a reset change in the agl_shell destructor, a
reset which is implicitly being done when the correct operations for the
protocol specifications have been applied.

Bug-AGL: SPEC-4503
Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
Change-Id: Ie87ce3b937f041a5704407593f580895f188ef56