Set paramiko.transport error level back to CRITICAL

Revert sha:6723502b07b66a0df1ef08bba484b6f46fe4d6f0

paramiko.transport is too noisy.
Removed cache flush on handling new connection

This was reducing the effectivity of the shared cache.

Because we use a fork model for our server there's no benefit on flushing
when per-process local cache was used (non memcached).

This is an error introduced when ported to ftp-cloudfs 0.21 interface.
tidying comments
use latest ftp-cloufds
ready for release 0.8.1