BrainScaleS: Fix segfault on exit() and provide run environment in install tests

We did introduce a new segfault-on-exit() in !244 (merged) when updating our dependency on log4cxx. Previously, singleton logger instances where referred to by raw pointers, now it's a non-POD type; using the static keyword on those types isn't safe → multiple destruction happens → fixed by removing global instances and using the log4cxx-internal reference counting.

Install tests don't seem to use the environment provided by def setup_run_environment(…). We work around this by providing the necessary PYTHONPATH environment variable modification in the test routine.