abrt-dump-oops: if backtrace is not seen, file an one-line oops

This allows to catch "Machine Check Exception:" oopses.
Also, one of our "not_oops" testcases _is_ a kernel bug,
and with this change it is caught too.

Added a test for MCE oops and tested it.

Fixed one outdated oops trst (nmi_oops_hash.right).

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>