Upgrade to Ehcache 2.10.6

[bclozel]

[snicoll]

This should have been applied to 1.5.x.

[wilkinsona]

I am not yet certain, but it looks like 2.10.6 is a breaking change as it seems to require Java 8.

[wilkinsona]

2.10.6 does indeed require Java 8. It uses ehcache-parent:2.22 which switched to building with Java 8 by default. 2.10.6 is also unusual as, at the time of writing at least, the version on JIRA does not contain any issues.

I think we should revert the upgrade to 2.10.6 in 1.5.x until we get some guidance from the EhCache team.