virsh: Add message to terminal when running snapshot-revert

virsh: Add message to terminal when running snapshot-revert

When running virsh snapshot-* command, such as snapshot-create-as /
snapshot-delete, it prints a result message.
On the other hand virsh snapshot-revert command doesn't print a result
message.

So, This patch fixes to add message when running virsh snapshot-revert
command.

    # virsh snapshot-create-as vm1 test1
    Domain snapshot test01 created
    # virsh snapshot-revert vm1 test1

    # virsh snapshot-delete vm1 test1
    Domain snapshot test01 deleted

Signed-off-by: Haruka Ohata <ohata.haruka@fujitsu.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Ján Tomko <jtomko@redhat.com>