MULE-7010: Implementation of clear() method in ObjectStore

improving tests

(cherry picked from commit 1566efdc3586951a6e01862742507d98ff42c122)

Conflicts:
	core/src/main/java/org/mule/util/store/MuleObjectStoreManager.java
	core/src/test/java/org/mule/util/store/MuleObjectStoreManagerTestCase.java
	tests/functional/src/main/java/org/mule/tck/util/FakeObjectStore.java
MULE-7463: Monitored ObjectStores should behave consistently

(cherry picked from commit 5e1449a2bb10981c3ed9b4744b0a2890fb2ed960)

Conflicts:
	core/src/main/java/org/mule/api/store/ObjectStoreManager.java
	core/src/test/java/org/mule/tck/probe/JUnitProbe.java
	core/src/test/java/org/mule/util/store/MuleObjectStoreManagerIntegrationTestCase.java
	distributions/standalone/src/main/resources/MIGRATION.txt
	modules/devkit-support/src/main/java/org/mule/security/oauth/DefaultRefreshTokenManager.java
Merge with 5e1449a2bb10981c3ed9b4744b0a2890fb2ed960
MULE-7728: Fixed several clean up problems related to partitioned object storages.

(cherry picked from commit 6b0fe2a5c68f54038e80c1be5ecd52733ad255f5)

Conflicts:
	core/src/main/java/org/mule/util/store/MuleObjectStoreManager.java
	core/src/main/java/org/mule/util/store/PartitionedPersistentObjectStore.java
	core/src/test/java/org/mule/util/store/MuleObjectStoreManagerTestCase.java