sstate.bbclass: update missed sstate event

sstate.bbclass: update missed sstate event

This is a patch to update the missed sstate event with
info about the sstate files locations that were found.
It's needed as to display the found file in the toaster ui.

Also fixes a bug where a setscene task may have appeared in the
missed list even if it was found in a sstate mirror.

(From OE-Core rev: ad66cd521d3e661dd57c5aa02c204585101984f3)

Signed-off-by: Alexandru DAMIAN <alexandru.damian@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>