Merge branch stable-2.15 into master
* origin/stable-2.15:
Use java.util.concurrent.ScheduledThreadPoolExecutor for tests
Document that cache cleaning intervals < 1h are not supported
Apply changes to file-based websession cache from HA-plugin
Update cache cleaner to HA-plugin version and add tests
Add additional tests for websession cash from HA-plugin
Refactor test key assignment in cache tests
Use junit to provide a temporary directory for testing
Simplify cache-directory creation
Adapt system time manipulation to method used in HA-plugin
Reformat code with google-java-format 1.7
Fix getIfPresentObjectNonStringTest
Change-Id: Ibca0bd25bb008bbf9f3a635398d517dfba4b0efe
