Backport HST session pools should be cleared after any change below /hippo:configuration

When a change below /hippo:configuration happens, odds are this is in the area of the security domains. Only newly created sessions will 'see' changes in security (for example a changed hippo:domain). Existing jcr sessions won't get these changes pushed.

Since a jcr session in a hst pool can live forever (certainly in low traffic sites), this means, a change in security domains might never make it to a hst pooled session as long as the application is not restarted.

I think we can better clear all sessions in all pools after any change below /hippo:configuration