monitor/hmp-cmds: improvements for the 'info migrate'

monitor/hmp-cmds: improvements for the 'info migrate'

When running:

(qemu) info migrate
globals:
store-global-state: on
only-migratable: off
...
xbzrle transferred: 640892 kbytes
xbzrle pages: 16645936 pages
xbzrle cache miss: 1525426
xbzrle cache miss rate: 0.09
xbzrle encoding rate: 91.42
xbzrle overflow: 40896
...
compression pages: 377710 pages
compression busy: 0
compression busy rate: 0.00
compressed size: 463169457
compression rate: 3.33

Add units for 'xbzrle cache miss' and 'compressed size',
make it easier to read.

Suggested-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Mao Zhongyi <maozhongyi@cmss.chinamobile.com>
Message-Id: <20200603080904.997083-8-maozhongyi@cmss.chinamobile.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>