Sshutils refactoring

Paramiko sftp client is not eventlet friendly. Also it doesn't work
with some servers, so upload/download methods has been removed.
Downloading or uploading can be done in other way (see examples).

Added ability to pass process stdin, which makes possible to
do on remote host anything at all.

Much more clean and usable API.

Change-Id: If357a2878c2c60646a975c386a0fe2f1616aec95
Merge "Sshutils refactoring"