Fix memory retaining by clearing listeners in groups.

The group listeners usually contain references to the bundle using the group, and given zk watches are kept in memory, we need to remove those references.
Fix fabric8-karaf distribution which is missing a file, leading to failures to provision remote ssh containers
Fix timestamp formatting for insight metrics on elasticsearch
Avoid possible NPE
Fix memory problem to remove a reference to ES when the servlet is destroyed.

The servlet is retained by pax-web servlet events.