DBLog test are bound to other test

# Description

The test_dblog.py check the content of the database during the test, running the test_dblog.py will always success because the database will be empty, but if other tests are runned before, the state of database may change and it may change the result of the test.

I think the test should be accurate, even if it's run alone or with other tests.

# Environment

- operating system:
- Python version:
- PyWPS version:
- source/distribution
- [x] git clone
- [ ] Debian
- [ ] PyPI
- [ ] zip/tar.gz
- [ ] other (please specify):
- web server
- [x] Apache/mod_wsgi
- [ ] CGI
- [ ] other (please specify):

# Steps to Reproduce

run `pytest tests/test_dblog.py` alone.

# Additional Information