Add support for installing server and agent via official packages

Added support for installing the server, database and agent agent via official packages from repo.zabbix.com.
Attributes:

* `node['zabbix']['major_version']` -- Major version to install packages from. Defaults to 2.2
* `node['zabbix']['agent']['install_method'] = 'package'` -- install agent via package
* `node['zabbix']['server']['install_method'] = 'package'` -- install server via package
* `node['zabbix']['server']['version'] = '2.2.1'` -- Server package version (used for database SQL scripts)

Updated Vagrantfile to install server and agents via package as well as agent via source:
* `zabbix-server` -- Zabbix server from package with Nginx and Postgresql
* `zabbix-agent` -- Zabbix agent from package
* `zabbix-src-agent` -- Zabbix agent from source

Also updated Berksfile to do the following:
* lock `yum` version earlier than 3.0 due to breaking changes in the yum cookbook (this should be updated to use `yum_epel` instead
* Lock `postgresql` to 3.2.0, due to https://github.com/hw-cookbooks/postgresql/issues/94
* Use `php_fpm` from a different provider until https://github.com/yevgenko/cookbook-php-fpm/issues/26 is fixed