Test suite should warn about skipped tests

[Andreas Hasenack]

The test suite should warn somewhere whenever tests are skipped, either because of a missing python module or just because the right env var was not set.

For example, the fact that the django tests were not run is not noted at the end, nor is this considered a failure or error:
[tests/django/stores.py]
Traceback (most recent call last):
  File "/home/andreas/canonical/launchpad-storm/therve/variable-leak/tests/django/stores.py", line 25, in <module>
    from django import conf
ImportError: No module named django

Also, when postgres and mysql URIs are not exported as env vars, several tests are just skipped. This should also be noted somewhere.

[James Henstridge (jamesh)]

The unittest framework doesn't support statuses other than success, failure or error. So we'd either need to implement this feature ourself, or make use of a unittest extension that has already done so (e.g. Trial, or jml's testtools when it gets the feature).