Change stomp.py disconnect() to stop()

- Change close_connection method from using disconnect() to stop() as the
  latter actually waits for the connection thread to exit after calling
  disconnect() itself.
Add TMPDIR env variable to Travis file

- Add exporting of TMPDIR env variable (where TMPDIR=$PWD/tmp) to Travis
  file so that tests don't try to create temp files in an unwritable area.
Add creation of tmp dir to Travis file

- Add creation of tmp dir to Travis file as it looks like it needs the
  directory to exist before the tests can write to it.
Exclude test_crypto from Travis file

- Add test_ssm to integration test and disable discoery so that
  test_crypto is exluded.
- Enable buffered output on unittests so that output is appeneded to
  failure messages.
- Reformat error message in test_crypto.
Merge pull request #6 from apel/issue_4-connection_threading

Stomp.py connection exit