virt: Fix login operation with vm without network interface.

It tries login over serial interface and don't waste time with
trying logging over net interface.

Signed-off-by: Jiří Župka <jzupka@redhat.com>
virt: Allow set network interface parameters none.

Signed-off-by: Jiří Župka <jzupka@redhat.com>
virt: Adds support for other get time methods.

adds hwclock and makes date more precisely.

Signed-off-by: Jiří Župka <jzupka@redhat.com>
virt: Adds support for kernel extra params

kernel_extra_params = " ..."

Signed-off-by: Jiří Župka <jzupka@redhat.com>
virt: Adds timedrift test without network interface.

test:
   guest_suspend
   guest_pause_resume

Signed-off-by: Jiří Župka <jzupka@redhat.com>