setmaxmem: add the new options to "virsh setmaxmem" command

setmaxmem: add the new options to "virsh setmaxmem" command

This patch adds the new options (--live, --config, and --current) to
"virsh setmaxmem" command. The behavior of above options is the same
as that of "virsh setmem".  When the --config option is specified, a
modification is effective for the persistent domain, while the --live
option is specified, a modification is effective for an active
domain. The --current option is specified, it affects a current
domain.

Signed-off-by: Taku Izumi <izumi.taku@jp.fujitsu.com>