Reading persistence.xml <exclude-unlisted-classes> properly

<exclude-unlisted-classes> is read incorrectly in
PersistenceUnitReader. Changed PersistenceUnitReader to follow the
rules set forth in the JPA specification.

Issue: SPR-10767
Merge remote-tracking branch 'origin/SPR-10767' into SPR-10767

Conflicts:
	spring-orm/src/main/java/org/springframework/orm/jpa/persistenceunit/PersistenceUnitReader.java