Disable sandboxing for XibCompile actions.

Fixes #2189.

The other idea of making the path that ibtoold wants to write to read-write in the sandbox strategy didn't seem to help (but I don't know why) - it randomly works or doesn't work, with or without that change.

--
PiperOrigin-RevId: 142553982
MOS_MIGRATED_REVID=142553982

src/main/java/com/google/devtools/build/lib/rules/objc/BundleSupport.java

@@ -341,6 +341,8 @@ private void registerConvertXibsActions(ObjcProvider objcProvider) {
               .setCommandLine(ibActionsCommandLine(archiveRoot, zipOutput, original))
               .addOutput(zipOutput)
               .addInput(original)
+              // Disable sandboxing due to Bazel issue #2189.
+              .disableSandboxing()
               .build(ruleContext));
     }
   }