allow configurable paramiko logging level

Since ever instance._ssh_connect call sets and resets paramiko logging level to INFO, any consumer of pycloudlib gets logging spam for every single cmd execution making it tough to sift though CI logs.

Let's make logging level configurable on the cloud, and reflect that logging level to dependencies like paramiko if called/setup.
Otherwise your CI runs look like:
```
INFO:paramiko.transport:Connected (version 2.0, client OpenSSH_6.6.1p1)
INFO:paramiko.transport:Authentication (publickey) successful!
INFO:paramiko.transport.sftp:[chan 0] Opened sftp connection (server version 3)
--- Push /tmp/pr_source.tar.gz -> i-0fb3543500b23e7b6:/tmp
---- Pull i-0fb3543500b23e7b6:/tmp/ubuntu-advantage-pro.deb /tmp/
--- Pull i-0fb3543500b23e7b6:/tmp/ubuntu-advantage-tools.deb /tmp/
/INFO:paramiko.transport.sftp:[chan 0] sftp session closed.

--- Launching VM to create a base image with updated ubuntu-advantage
--- Launching AWS PRO image ami-0a64b4493bc9dc321(trusty)
/INFO:paramiko.transport:Connected (version 2.0, client OpenSSH_6.6.1p1)
INFO:paramiko.transport:Authentication (publickey) successful!
|--- aws PRO instance launched: i-0f3fd86752859bcb4. Waiting for ssh access
\INFO:paramiko.transport:Connected (version 2.0, client OpenSSH_6.6.1p1)
|INFO:paramiko.transport:Authentication (publickey) successful!
INFO:paramiko.transport.sftp:[chan 0] Opened sftp connection (server version 3)
INFO:paramiko.transport.sftp:[chan 0] sftp session closed.
INFO:paramiko.transport:Connected (version 2.0, client OpenSSH_6.6.1p1)
INFO:paramiko.transport:Authentication (publickey) successful!
INFO:paramiko.transport.sftp:[chan 0] Opened sftp connection (server version 3)
INFO:paramiko.transport:Connected (version 2.0, client OpenSSH_6.6.1p1)
INFO:paramiko.transport:Authentication (publickey) successful!
/INFO:paramiko.transport.sftp:[chan 0] sftp session closed.
--- Creating base image snapshot from vm i-0f3fd86752859bcb4
INFO:paramiko.transport:Connected (version 2.0, client OpenSSH_6.6.1p1)
INFO:paramiko.transport:Authentication (publickey) successful!
\INFO:paramiko.transport:Connected (version 2.0, client OpenSSH_6.6.1p1)
INFO:paramiko.transport:Authentication (publickey) successful!

```