remote handler for virDomainGetCPUStats()

remote handler for virDomainGetCPUStats()

Unlike other users of virTypedParameter with RPC, this interface
can return zero-filled entries because the interface assumes
2 dimensional array. We compress these entries out from the
server when generating the over-the-wire contents, then reconstitute
them in the client.

Signed-off-by: Eric Blake <eblake@redhat.com>