Support jpa enhancement of java 8 classes

[gallardo]

OpenJPA 2.2 doesn't support enhancement for Java 8 classes (see https://issues.apache.org/jira/browse/OPENJPA-2386)

[gallardo]

OpenJPA 2.2 doesn't support enhancement for Java 8 classes (see https://issues.apache.org/jira/browse/OPENJPA-2386):

Execution failed for task ':enhance'.
> java.lang.IllegalArgumentException

This issue is solved in OpenJPA 2.4.

Unfortunately, gradle cannot pull maven transitive dependencies, so we have to explicitly add org.apache.xbean:xbean-asm5-shaded. (Alternatively, org.apache.openjpa:openjpa-all:2.4.0 has all needed dependencies, but I opted for the lightest dependencies declaration).

We'll still see warnings though, due to https://issues.apache.org/jira/browse/OPENJPA-2300.

Detailed stacktrace snippet for the record:

ant:openjpaenhancer] java.lang.IllegalArgumentException
[ant:openjpaenhancer]   at org.objectweb.asm.ClassReader.<init>(Unknown Source)
[ant:openjpaenhancer]   at org.objectweb.asm.ClassReader.<init>(Unknown Source)
[ant:openjpaenhancer]   at org.objectweb.asm.ClassReader.<init>(Unknown Source)
[ant:openjpaenhancer]   at org.apache.openjpa.enhance.AsmAdaptor.toJava7ByteArray(AsmAdaptor.java:93)
[ant:openjpaenhancer]   at org.apache.openjpa.enhance.AsmAdaptor.writeJava7(AsmAdaptor.java:84)
[ant:openjpaenhancer]   at org.apache.openjpa.enhance.AsmAdaptor.write(AsmAdaptor.java:54)
[ant:openjpaenhancer]   at org.apache.openjpa.enhance.PCEnhancer.record(PCEnhancer.java:633)
...