hotfix for mongo tests

Fixes the edge case where the mongodb extension is installed but the mongodb server isn't running or available, resulting in a fatal error in class teardown and a failing rather than skipped construct test. 

Causing the construct test to be skipped rather than fail is kindof a system-specific decision based on whether the normal state should be 'running' or not. So that really should ultimately be based on a config option somewhere that indicates whether the system expects and depends on a mongo server running. Wasn't quite sure where to get that from.