bitbake: lib/bb/runqueue.py: fix exceptions with -k and failed targets

bitbake: lib/bb/runqueue.py: fix exceptions with -k and failed targets

If a target dependency is marked as failed and yet we are continuing on
because -k has been specified, don't try to access the dependency's data
in taskData.build_targets since it will have been removed. This fixes
"IndexError: list index out of range" errors in this situation.

Also, do not print the "unhandled exception" message when SystemExit is
raised since we will have reported the actual error already in this
case (e.g. when -k has been specified and some targets failed).

Fixes [YOCTO #3133].

(Bitbake rev: 70eebc184eb1ab3678be87bed019b5beadecdc89)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>