MULE-6809 - changing persistent object store implementation to avoid using keys as filenames
(cherry picked from commit 6e1730d166559767c3d9419d814d1eb66aec1ea6)

Conflicts:
	core/src/main/java/org/mule/util/store/PartitionedPersistentObjectStore.java
(cherry picked from commit 1d1990354d038578e7e35b9b2f8ad7dd4daba188)