This makes a couple of key changes to help diagnose issues in rbssh.
--version now shows the Python version and the Review Board package

location, to help ensure that the right version is being run.
Warnings are now disabled at the top of the module, before we import

anything that may warn. This helps avoid some bad output that can occur,

depending on versions of packages and Python, particularly with

Cryptography.

Verified that this got rid of warnings that messed up test output.
Verified that --version showed the correct information.