Don't use paramiko library for SSH connections to the Runner, but
instead execute the `ssh` command using Subprocess.
When one uses SSH ID files protected by password, the paramiko library
can not access them without it, even if the password is stored in the
ssh-agent running in the user session. On the other hand, running the
`ssh` command using Subprocess works just fine in this scenario.
Signed-off-by: Tomas Hozza <thozza@redhat.com>