virsh: suppress aliases in group help

'virsh help | grep nodedev-det' shows only nodedev-detach, but
'virsh help nodedev | grep nodedev-det' also shows the old alias
nodedev-dettach that we intentionally hid in commit af3f9aab.

See also commit 787f4feb and this bug report:
https://bugzilla.redhat.com/show_bug.cgi?id=956966

* tools/virsh.c (vshCmdGrpHelp): Copy suppression of vshCmdHelp.
Signed-off-by: NEric Blake <eblake@redhat.com>

tools/virsh.c

@@ -1177,6 +1177,8 @@ vshCmdGrpHelp(vshControl *ctl, const char *grpname)
                  grp->keyword);
 
         for (cmd = grp->commands; cmd->name; cmd++) {
+            if (cmd->flags & VSH_CMD_FLAG_ALIAS)
+                continue;
             vshPrint(ctl, "    %-30s %s\n", cmd->name,
                      _(vshCmddefGetInfo(cmd, "help")));
         }