jersey-media-moxy 2.18 onwards + GAE/J raises NoClassDefFoundError

The combination of jersey-media-moxy 2.18 onwards and Google App Engine for Java raises NoClassDefFoundError with an error message _"javax.naming.InitialContext is a restricted class. Please see the Google App Engine developer's guide for more details."_

Below is a part of the stack trace.

```
Caused by: java.lang.NoClassDefFoundError: javax.naming.InitialContext is a restricted class. Please see the Google App Engine developer's guide for more details.
at com.google.appengine.tools.development.agent.runtime.Runtime.reject(Runtime.java:52)
at org.eclipse.persistence.jaxb.Concurrent$GetManagedExecutorService.compute(Concurrent.java:54)
at org.eclipse.persistence.internal.cache.Memoizer$1.call(Memoizer.java:44)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at org.eclipse.persistence.internal.cache.Memoizer.compute(Memoizer.java:51)
... 78 more
```

Java classes that can be used in Google App Engine are listed in [The JRE Class White List](https://cloud.google.com/appengine/docs/java/jrewhitelist).

jersey-media-moxy 2.17 does not raise this error.
#### Affected Versions
[2.18, 2.22.1]