Extend VLOG(signals) to be more useful.

-verbose:signals was pretty useless because it didn't tell you much
about what the signal being examined actually was. Extend HandleFault
logging to include details about the signal being handled.

Test: ./test/run-test --runtime-option -verbose:signals --host --dev 983
Change-Id: I78baca685623c6b37f8148d6eeb2614c38fdfa69