tests/tools_dbmaint_unittest.py test problems

[Lars Butler]

Two issues:

1) The expected results in 'test_run_cmd_with_errors' and 'test_run_cmd_with_errors_and_ignore_exit_code' are Linux-specific outputs; these tests fail on OSX dev machines.
2) tools_dbmaint_unittest.py is not actually run as part of the whole test suite (run_tests.py, for example), which is why didn't catch this problem earlier. One way to fix this is to add 'from tools_dbmaint_unittest import *' to tests/__init__.py

[Lars Butler (lars-butler)]

Pull request: https://github.com/gem/openquake/pull/402