Except LXC and UML driver, implementations of all other drivers
simply return 0, because these drivers doesn't have config both
in memory and on disk, no need to track if the domain of these
drivers updated or not.

Rename "xenUnifiedDomainisPersistent" to "xenUnifiedDomainIsPersistent"

* esx/esx_driver.c
* lxc/lxc_driver.c
* opennebula/one_driver.c
* openvz/openvz_driver.c
* phyp/phyp_driver.c
* test/test_driver.c
* uml/uml_driver.c
* vbox/vbox_tmpl.c
* xen/xen_driver.c
* xenapi/xenapi_driver.c