Introduce public API for domain async job handling

Introduce public API for domain async job handling

Introduce a new public API that provides a way to get progress
info on currently running jobs on a virDomainpPtr. APIs that
are initially within scope of this idea are

 virDomainMigrate
 virDomainMigrateToURI
 virDomainSave
 virDomainRestore
 virDomainCoreDump

These all take a potentially long time and benefit from monitoring.
The virDomainJobInfo struct allows for various pieces of information
to be reported

 - Percentage completion
 - Time
 - Overall data
 - Guest memory data
 - Guest disk/file data

* include/libvirt/libvirt.h.in: Add virDomainGetJobInfo
* python/generator.py, python/libvirt-override-api.xml,
  python/libvirt-override.c: Override for virDomainGetJobInfo API
* python/typewrappers.c, python/typewrappers.h: Introduce wrapper
  for unsigned long long type