[10.1.x] Invalidate session doesn't remove it from jetty cache

[grgrzybek]

Backport of #2109

[grgrzybek]

Something's different than in ee10...

[grgrzybek]

Jetty 12.1.3 upgrade in Pax Web 10 (ee8) failed with strange errors (in default servlet, imagine...), so I'm postponing this to 10.1.0.