Changed the default `pid_path` attribute to "/usr/local/var/run"

On some system, contents of `/var/run` (and possibly `/usr/local/var/run`) is cleared on restart;
http://askubuntu.com/questions/89352/does-ubuntu-periodically-clean-empty-directories-under-var-run.

As discussed in #115 and #108, the solution is to simply ditch the `elasticsearch` prefix,
the PID files are based on node name anyway.

Closes cookbook-elasticsearch#108
Closes cookbook-elasticsearch#115
Updated the default Elasticsearch version to 0.90.10

See: http://www.elasticsearch.org/downloads/0-90-10/
README updates: Elasticsearch capitalization, `curl` command