Make sure logging works with threads properly

##### SUMMARY
The libssh callbacks and log level is stored in thread-local variables so if we spawn threads in python, we need to make sure to reinitialize logging to make sure it works properely.

##### ISSUE TYPE
- Feature Idea

##### ADDITIONAL INFORMATION
Based on discussion in #597 which introduces the logging.

Start by reading discussion #597 and tracing how the libssh callbacks and log level are stored in thread-local variables. Verify the behavior when Python threads are spawned and logging is reinitialized; done means callbacks and log levels work correctly across those threads.

Written by the indexing model from the issue text.