feature: Zabbix cookbook performance enhancements

1. There has been several Zabbix performance enhancements we've made
to a client environment that should be utilized moving forward as
part of the SRP. Since these improvements were made over the course 
of serval months, it will be hard to cherry-pick exact commits. 
Instead, the Zabbix cookbook has been completely replaced with the 
modified, new and improved cookbook. 
2. Some of these 'enhancements' are as follows:

* Make nginx load balance among multiple PHP processes to provide greater
concurrency for the zabbix_web subsystem. This makes the Zabbix web UI
much more responsive and capable of accommodating multiple concurrent users.

* Added ability to increase OS-provided shared memory capacity and make
zabbix_server subsystem utilize this additional shared memory.

Squashed commit of the following:

commit a592d9133e47b7573c08f2efbac73c1a773a03b4
Author: Rachel McCuistion <rachel@infochimps.com>
Date:   Thu Feb 13 22:43:34 2014 -0600

    version bump to 3.3.13

commit 624be2ff6a7e3acedac15469b3220713b2f18055
Author: Rachel McCuistion <rachel@infochimps.com>
Date:   Thu Feb 13 22:40:02 2014 -0600

    adding new, enhanced zabbix cookbook transplated from client org_cookbooks/zabbix

commit fdb1a3228d2a0c3faacac8280a695b8ea5180cf2
Author: Rachel McCuistion <rachel@infochimps.com>
Date:   Thu Feb 13 22:38:10 2014 -0600

    removing old zabbix cookbook; preparing to upload the new, enhanced zabbix cookbook

Change-Id: Id724593f95b9b1ff4c0c9d450e9670486e1444ff
Merge "feature: Zabbix cookbook performance enhancements"