qemu.test: rework timedrift_adjust_time releated case

Update:
    1. use epoch time to avoid timezone convert issue.
    2. use OS build-in shell to adjuest host/guest clock.
    3. use private brige to avoid guest sync time from network.
    4. remove s4 releated configuration.

Signed-off-by: Xu Tian <xutian@redhat.com>