Implement public API for virDomainGetIOThreadsInfo

Implement public API for virDomainGetIOThreadsInfo

Add virDomainGetIOThreadInfo in order to return a list of
virDomainIOThreadInfoPtr structures which list the IOThread ID
and the CPU Affinity map for each IOThread for the domain.

For an active domain, the live data will be returned, while for
an inactive domain, the config data will be returned.

The API supports either the --live or --config flag, but not both.

Also added virDomainIOThreadsInfoFree in order to free the cpumap
and the IOThreadInfo structure.

Signed-off-by: John Ferlan <jferlan@redhat.com>