ehcache-core dependency is missing from the pom.xml file. The dependency currently needs to be externally defined when clearpass is added to an overlay pom.
A possible fix would be to include ehcache-core in the dependency management section of the parent pom so that inheriting modules such as ehcache ticket registry and clearpass can benefit from.
Merged though I believe it was merged into master, which is 4.0.x?
Updated the fix version.