virsh: correct return value error

Fix cmdDomblklist to return 'true' on success instead of '0'

https://bugzilla.redhat.com/show_bug.cgi?id=758590Signed-off-by: NAlex Jia <ajia@redhat.com>

tools/virsh.c

@@ -1745,7 +1745,7 @@ cmdDomblklist(vshControl *ctl, const vshCmd *cmd)
         VIR_FREE(source);
     }
 
-    ret = 0;
+    ret = true;
 
 cleanup:
     VIR_FREE(disks);