history-etl: service: update discovery of JAVA_HOME

The new implementation uses engine's script
/usr/share/ovirt-engine/bin/java-home to detect JAVA_HOME
location.

Change-Id: I34dd5891cfc76242bb3bb50bf77bb48ad50839c8
Bug-Url: https://bugzilla.redhat.com/1019178
Related-To: https://bugzilla.redhat.com/1009863
Signed-off-by: Alex Lourie <alourie@redhat.com>