Returns exit code 1 if at least one test failed.

It should make travis-ci to report test failures when they actually fail.
Ie. build 169.1 has test failures, but build was happily reported as Passed,
this patch should change this.
Merge pull request #210 from zas/test_exit_code

Ensure setup.py returns non-zero exit code on test failure
Apply patch provided by zas
Merge pull request #211 from Sophist-UK/sophist_fix_nat_refresh

Fix errors on refresh of NAT track (PICARD-549)