fixes #25 - dbname check always fails

@twobraids r?
but when used with Socorro, this will have to work with dbname = 'socorro_integration_tests' and who knows what other users of this class will want to use.

I suggest that you do something like this so that users can override this setting...

``` python
    def ensure_using_test_database(self):
        if not ('dbname=test' in dsn or 'dbname=travis_ci_test' in dsn):
            raise ValueError(
                'test database must be called test_ something '
                '(or travis_ci_test) or '
                'else there is a risk you might be testing against a '
                'real database'
            )

    def setUp(self):
        # ...
        dsn = (
            'host=%(database_hostname)s '
            'dbname=%(database_name)s '
            'user=%(database_username)s '
            'password=%(database_password)s' % self.config.crontabber
        )
        self.ensure_using_test_database()
        self.conn = psycopg2.connect(dsn)
        # ....
```

That gives future clients the ability to override that function so that it will accept whatever the name of the test database.