buildbot test failures

[John W. Eaton]

I recently made some changes so that buildbot builds report success only 
if the number of failed tests is exactly 0.  You can see here

  buildbot.octave.org:8010

that we currently aren't doing so well.

On the system that runs the following builders

  gcc-fedora
  gcc-lto-fedora
  clang-fedora

some tests fail because of a current fedora bug in osmesa.  I suppose I 
could (temporarily) disable osmesa on those systems to eliminate the 
failures.

On the system that runs the following builders

  gcc-6-debian
  clang-3.9-debian

8 tests are failing because there is no audio device.  I could skip 
those tests if there were a way to check whether audio devices are 
available, but I'm not sure how to do that.  Currently, audiodevinfo 
throws an error if there is no audio device.  Would it be OK to change 
that so it simply returns an empty structure?  For my purposes that 
would make checking easier, but I'm not sure whether it will cause other 
trouble.

The clang-osx build fails because of a problem with integer typedefs 
that I reported here:

  https://savannah.gnu.org/bugs/?50510

The gcc-6-lto-debian build fails because of a mysterious problem saving 
and loading signed 32-bit integers to HDF5 files.

And finally, the mxe-native-on-debian build is failing because the 
of-database package configure script is failing with the following message:

  checking for PQconnectdb in -lpq... no
  configure: error: unable to find the PQconnectdb() function in pq

but I think that's just a missing package problem on my build system, so 
I'll fix that and try again.

I'd like to eliminate these failures in some way so that we can expect 
to see all builds regularly succeeding.  If failures are rare, then I 
think we can be more sure that regressions are noticed soon after they 
happen.

Comments, suggestions, and help are all welcome.

Thanks,

jwe