virsh: Update the help information for undefine command.

virsh undefine command can now undefine an active guest, but the help information is still the old.
This patch modifies it and make it coincident to the manpage of virsh.
Signed-off-by: Ntangchen <tangchen@cn.fujitsu.com>

AUTHORS

@@ -195,6 +195,7 @@ Patches have also been contributed by:
   Xu He Jie            <xuhj@linux.vnet.ibm.com>
   Lei Li               <lilei@linux.vnet.ibm.com>
   Matthias Witte       <witte@netzquadrat.de>
+  Tang Chen            <tangchen@cn.fujitsu.com>
 
   [....send patches to get your name here....]
 

tools/virsh.c

@@ -1897,8 +1897,9 @@ cmdDefine(vshControl *ctl, const vshCmd *cmd)
  * "undefine" command
  */
 static const vshCmdInfo info_undefine[] = {
-    {"help", N_("undefine an inactive domain")},
-    {"desc", N_("Undefine the configuration for an inactive domain.")},
+    {"help", N_("undefine a domain")},
+    {"desc",
+     N_("Undefine an inactive domain, or convert persistent to transient.")},
     {NULL, NULL}
 };