snapshot: expose --running and --paused in virsh

snapshot: expose --running and --paused in virsh

Pretty straight-forward exposure of new flags.  For most commands,
we let the API reject mutually exclusive flags; but for save-image-edit,
we do the sanity check ourselves to avoid looping on flag failure if
the edit cycle is ever enhanced to allow the user to retry an edit
to fix up an xml validation error.

* tools/virsh.c (cmdManagedSave, cmdRestore, cmdSave)
(cmdSaveImageDefine, cmdSaveImageEdit): Add new flags.
* tools/virsh.pod (managedsave, restore, save, save-image-define)
(save-image-edit): Document them.