Various fixes to generated .deb packages

This resolves a few inconsistencies and issues in the generated packages
for Debian/Ubuntu:

  * Creates /etc/logstash/conf.d
  * Installs a basic defaults file in /etc/default/logstash (which also sets HOME)
  * Stops creating /var/run/logstash (unused)
  * Uses /var/lib/logstash as the home directory of the logstash user instead of /home/logstash
  * Defaults package files to be owned by root, fixes ownership in post-install script
  * Properly stops service when removing the package on Debian

The end result is that after installing, LogStash will pretty much "just
work" with only 2 changes:

1) Enable START=yes in /etc/default/logstash
2) Provide a config for the LogStash agent
Create and package an init script for logstash-web