Introduce command 'virsh domstats --dirtyrate' for reporting memory
dirty rate information. The info is listed as:
Domain: 'vm0'
dirtyrate.calc_status=2
dirtyrate.calc_start_time=1534523
dirtyrate.calc_period=1
dirtyrate.megabytes_per_second=5
Signed-off-by: Hao Wang <wanghao232@huawei.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>