Debian/Redhat package improvments

This decision helps people who want to rollout the oracle java without having an openjdk java installed.

* Removed any hard dependency on Java in the debian package
* The debian init script does not check for an existing JAVA_HOME anymore
* Debian and RedHat initscripts now exit if they do not find a java binary (instead of starting elasticsearch in the background and swallowing the error as there is no way to log it in that case)
* Changed the debian init script to rely on the pid file instead of the argument name of process
* Added a useful error message in case no java binary is available (in elasticsearch shell script)

Closes #3304
Closes #3311