Fix lightmediascanner systemd service to avoiding a race
condition with /var/volatile/tmp on the first boot by running it
after run-agl-postinsts.service. Furhtermore, for extra safety,
a restart on failure has been added.
Bug-AGL: SPEC-2869
Change-Id: Ib0cadfaa3b4da2a15ac3cfc04cf6d8174e63eb63 Signed-off-by: Leon Anavi <leon.anavi@konsulko.com>