This patch adds the --current option to "virsh setvcpus"
command. Currently "virsh setvcpus" command supports
"--live" and "--config" , but "--current" option.
From view of consistency, it's reasonable to support
"--current" option too.

When --current is specified, it affects a "current"
domain.
Signed-off-by: NTaku Izumi <izumi.taku@jp.fujitsu.com>