blockjob: support new BLOCK_JOB_2 event

blockjob: support new BLOCK_JOB_2 event

Libvirt 1.2.6 is introducing a new block job event that passes disk
information by target device rather than host file name.  At the
python level, we are just a passthrough, so we can reuse all the
existing code and just wire up the new enum value.

* libvirt-override-virConnect.py
(_dispatchDomainEventBlockPullCallback): Rename...
(_dispatchDomainEventBlockJobCallback): ...to this, and make
generic to both events.
* libvirt-override.c
(libvirt_virConnectDomainEventBlockJobCallback): Match naming.
(libvirt_virConnectDomainEventRegisterAny): Allow new registration.

Signed-off-by: Eric Blake <eblake@redhat.com>