Add decorator to check Fuel statistics sending

Add new decorator which can parse test docstring to
determine what actions were performed during the test and
then check that they were logged and sent to statistics
collector service properly.
It expects that collector host permit login via SSH using
RSA key located in user's home directory.
If sending of usage stats isn't enabled in tests, decorator
will check that statistics wasn't sent.
Also verify the absence of private info (e.g. passwords,
IPs, nodes names) in collected data.

Change-Id: Ia79ca9deef436357bcec19e78611c3b228874e63
Implements: blueprint fuel-stats-test
Merge "Add decorator to check Fuel statistics sending"