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

attributes/default.rb

@@ -33,7 +33,7 @@
 default.elasticsearch[:path][:data] = "/usr/local/var/data/elasticsearch"
 default.elasticsearch[:path][:logs] = "/usr/local/var/log/elasticsearch"
 
-default.elasticsearch[:pid_path]  = "/usr/local/var/run/elasticsearch"
+default.elasticsearch[:pid_path]  = "/usr/local/var/run"
 default.elasticsearch[:pid_file]  = "#{node.elasticsearch[:pid_path]}/#{node.elasticsearch[:node][:name].to_s.gsub(/\W/, '_')}.pid"
 
 # === MEMORY