BaseStoreTest.testPurgeExpired fails randomly

On some DB (like DB2, Oracle11gR1, ...) BaseStoreTest.testPurgeExpired sometimes fails on assertion error.

Investigated and found out that these stores don't insert all the entries in time before lifespan runs out and after that, there's a "contains" check which fails.

Resolution is to move the "contains" checking right after insertion and adjust slightly the lifespan and idle values, so the cache store can manage to insert entry in time. The goal is to stabilize the testsuite.