Default methods not allowed in PipelineOptions

If I create a class that extends PipelineOptions and contains a default method, the PipelineOptionsFactory will throw an exception because all non-static, non-synthetic and non-known methods need to have a getter and a setter.

For example, these PipelineOptions
```

public interface MyOptions extends PipelineOptions {
void setValue(String s);
String getValue();

default List getValues() {
return Arrays.asList(getValue().split(","));
}
}
```

will throw an exception in org.apache.beam.sdk.options.PipelineOptionsFactory.java:
```

private static void validateMethodsAreEitherBeanMethodOrKnownMethod(
Class
iface,
Class klass,
List descriptors) {

...
//
Verify that no additional methods are on an interface that aren't a bean property.
// Because methods
can have multiple declarations, we do a name-based comparison
// here to prevent false positives.
SortedSet
unknownMethods = new TreeSet<>(MethodComparator.INSTANCE);
unknownMethods.addAll(
Sets.filter(

Sets.difference(Sets.newHashSet(iface.getMethods()), knownMethods),
Predicates.and(

NOT_SYNTHETIC_PREDICATE,
input -> !knownMethodsNames.contains(input.getName()),

NOT_STATIC_PREDICATE)));
checkArgument(
unknownMethods.isEmpty(),
"Methods %s
on [%s] do not conform to being bean properties.",
FluentIterable.from(unknownMethods).transform(ReflectHelpers.METHOD_FORMATTER),

iface.getName());
}
```

Having a NOT_DEFAULT_PREDICATE in addition to the other predicates would allow 
```

private static final Predicate NOT_DEFAULT_PREDICATE = input -> !input.isDefault();

```

Seems like it would do the trick.

Imported from Jira [BEAM-8669](https://issues.apache.org/jira/browse/BEAM-8669). Original Jira may contain additional context.
Reported by: chrisstockton.