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
fix: Use nginx for zabbix

1. For more details
https://gist.github.com/mccuistion/092bd8b2bb7bc538e67c

commit 3f4b95a4deaaa25fb3a5358545fa095325a57499
Author: Alex Vinnik <alex.vinnik@infochimps.com>
Date:   Thu Mar 20 13:40:55 2014 -0500

    Use nginx for zabbix

    Change-Id: I95ec6d96c6bb8ee33cb1d0c2a1e59affa7a7828e

Change-Id: I47f76bd35b46401d04c071e3448e628fad6483eb
Revert "feature: Zabbix cookbook performance enhancements"

This reverts commit 75810debd8ac547577c2199e3db31851b3b8ea58.

Change-Id: Ie46d60a8ac83a33fe33e3c5905ac0fab9035867e
feature: airlifting Dhruv's zabbix optimizations

Change-Id: I4cf86186be0db6db75cff09d8ab4ac849f0c686f
Fix: Correct Double Discovery IP

This will break zabbix_agentd if unchecked

Squashed commit of the following:

commit 7418772251f5eec1e63d50c2e6b8e91cb08b107d
Author: Travis Dempsey <travis@infochimps.com>
Date:   Mon Mar 24 15:41:13 2014 -0500

    uniq discovered zabbix servers

    Change-Id: Ie5938b3f633a911da0518847af9331864cb7f038

Change-Id: I7cb0b959e8a420151afcbc5e645f00eba7a2600f
Merge pull request #43 from joshbronson/backport_zabbix_enhancements

Backport zabbix enhancements