vm-configurator: Sync clock to the host's configured timezone

When suspending/resuming or reverting to snapshots, the guest's time currently doesn't sync up with the host's.

By setting the domain clock offset to LOCALTIME we get the qemu guest agent to update the guest's clock to match the hosts.

We were already doing this for Windows guests.

See https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/virtualization_administration_guide/sect-virtualization-tips_and_tricks-libvirt_managed_timers

Fixes #704 (closed)