Empty page returned when login cookie with wrong IP address

1/ visit a wiki
2/ login
3/ change IP
4/ reload -> you get an empty page

This issue is related to the changes in MyPersistentLoginManager (I think in XWIKI-2206).
The server tries to delete all cookies from the domain and the parent domains.

This seems to fail in some containers (at least in Sun app server and Jetty)

We need to revert this code and change the system to have servers coexist on the same cookie domain. I suggest using a cookie prefix