DATAJPA-353 - Adjusted path resolving of mappingFileLocations(…) to conf...

...orm to the JPA spec.

Adjusted scanForMappingFileLocations(…) in ClasspathScanningPersistenceUnitPostProcessor to resolve the paths to class-path loadable paths.
Updated test case findsMappingFile accordingly.
Added test case shouldFindJpaMappingFilesFromMultipleLocationsOnClasspath and required resources to verify that mapping files with recursive wildcard pattern can be found from multiple locations in class path.