Fix error reporting when sandboxed process is signaled.

BUG=None
TEST=Unittests pass.
TEST=security_Minijail_seccomp passes on leon.
TEST=/usr/bin/yes; killall yes; echo $? prints 143.
TEST=minijail0 -- /usr/bin/yes; killall yes; echo $? prints 143 (not 253).
TEST=minijail0 -S /dev/null -- /usr/bin/yes; echo $? prints 253.

Change-Id: I62f779da9b5b3a61f6aff4c9855e5b73669c9efe
Reviewed-on: https://chromium-review.googlesource.com/195627
Reviewed-by: Nam Nguyen <namnguyen@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Commit-Queue: Jorge Lucangeli Obes <jorgelo@chromium.org>
2 files changed