fixes "su -" escalation

root_password was not being passed through from the RemoteClient
to the SSH client instantiation.

Change-Id: I4cd61821dd9fbe099bcdc2097807446d4072f9c4
Closes-Bug:#1362666
use native kill method on Popen object

Change-Id: Icf704164292637b92da25d8c720a72a5ca7c6ba6
Closes-Bug: 1381195