use netaddr module for mac address format conversion

Don't use custom function for mac address format
conversion, use netaddr module instead.
fix mac, given to set_mac_address format

Use parallels mac format for address, given to
set_mac_address method, else warnings could be shown
by prlctl.
use netaddr module to parse network address
fix type unplug_vifs -> _unplug_vifs in power_on
use prlsdkapi.Vm.refresh_config

There is a special function, which requests new VE configuration
from the server - refresh_config. So let's use it instead of
recreating Vm object.
Merge branch 'master' of test-vm:pcs-nova-driver