client.shared.aexpect: Add NoEchoShellSession

This class behaves the same as `ShellSession`, additionally it supports
terminals without echo. This could be used eg when interacting with
docker with `--tty=false`, or when you interact with shell with disabled
echo `"stty -echo"`.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>