Revert "CLOUDSTACK-7408: Fixed - Private key of the ssh keypair was getting corrupted"

This reverts commit e921ec6ec79c50096d58264d60c15091969ff888.

CLOUDSTACK-7408: sshClient.py - removing function load_host_keys(). This function is used to load host keys from local host keys file and to save back the host key. It is not needed while running test cases because we are connecting to unknown host anyway and don't want to use any local host key file. We have the AutoAddPolicy for missing host key file, hence whenever ssh connects to a new host, it will save the host key in memory temporarily.

Signed-off-by: SrikanteswaraRao Talluri <talluri@apache.org>