[libvirt] Allow to undefine a running domain

[Osier Yang]

Per API virDomainUndefineFlags' doc says, if a domain is running,
it will be converted to transient, but keep running. However,
the drivers prohibit one undefining a running domain. 

This patch series modify the internal domainUndefineFlags function
of all drivers (except some driver don't need to check if the
domain is running, it's handled by the underlying hypervisor, such
as ESX and XEND).

The principle is:

1) Set vm->persistent = 0 for a running domain
2) domainDestroy and domainShutdown will take care of remove the
domain obj from the hash table.

[PATCH 1/8] libxl: Allow to undefine a running domain
[PATCH 2/8] lxc: Allow to undefine a running domain
[PATCH 3/8] openvz: Allow to undefine a running domain
[PATCH 4/8] qemu: Allow to undefine a running domain
[PATCH 5/8] test: Allow to undefine a running domain
[PATCH 6/8] uml: Allow to undefine a running domain
[PATCH 7/8] vmware: Allow to undefine a running domain
[PATCH 8/8] xen: Allow to undefine a running domain (xm_internal)

Split the patches for easy reviewing, will merge when committing
if need.

Regards
Osier