This is mostly so BGMApp won't leave BGMDevice as the default if BGMApp
crashes, which would stop audio from playing until the user changed the
default device themselves. Also handles SIGINT, SIGTERM and SIGQUIT.
For crashes where the BGMApp process may be in an unknown state, e.g.
segfaults, BGMXPCHelper handles changing the default device.
Should fix the Travis Xcode 9 build, which is currently failing because
the AppleScript we use to quit BGMApp in .travis.yml gets "user
cancelled" for some reason.
Also makes some minor improvements to the reports generated by
CrashReporter. The way CrashReporter works with Background Music should
otherwise be unchanged.
Skipping them by overriding runTest didn't work and this is the only other way
I can think of. xcodebuild's -skip-testing option would work, but only with
recent versions of Xcode.
6.4 should already have been retired according to their documentation, so it
will probably need to be removed. But it would be nice to have because it's the
only OSX 10.10 image.
Also, log the installed audio devices and their audio IDs.
I think the tests are probably failing because the Travis VMs don't have
any audio devices. If so, this won't actually fix the tests, but it
should help us narrow it down.
