- Added a new host command nodecpumap
- Added documentation

Example:
$ virsh nodecpumap
CPUs present:  8
CPUs online:   3
CPU map:       y-y-y---
Signed-off-by: NViktor Mihajlovski <mihajlov@linux.vnet.ibm.com>
Signed-off-by: NEric Blake <eblake@redhat.com>