adding test for obspy-scan

* adding test for obspy-scan by comparing png output
* making obspy-scan more robust against sampling_rate=0 and funky station
  names
Adding warning for problematic ids
travis ping
Merge pull request #647 from mbyt/obspy-scan-tests

Obspy scan tests
print environment variables in travis

currently strange test problems in travis, this might help in the future
to check on changes/problems with environment variables.