init: Log local_boot_trigger output

Save the output of the local_boot_trigger to help debugging when this
does not work.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1082472
Change-Id: I8cf12b224ec166052d0c29212730b0a15a5ee0d6
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>