Call onRemoval of shard IdCache during clear.

This looks like a copy/paste issue where onCached was being called
rather than onRemoval. This should fix the ID cache stats not being
correct after a call to /_cache/clear?id_cache=true
Added test for verifying the id cache size if the clear cache api is invoked.
Debian init script: Add debian default java location

Adding /usr/lib/jvm/default-java to JAVA_HOME candidates to check

Closes #3500
cleanup removable of reject_policy
Dont write pidfile twice on startup

There is no need to write the pidfile in the bin/elasticsearchshell script
as this happens already in the java code.

Also cleaning up the bin/elasticsearch shell script a bit (no need to return
an error code when exec is called, as this forks and exits the shell script
immediately).

Closes #3529
Closes #1745