Refactors fuctionality from recipes/default.rb into recipes/common.rb
except for agent install

All recipes that require zabbix structure/user include_recipe
"zabbix::common" so that we can call into them at any level

default recipe delegates to agent recipe

agent recipe that follows the same pattern as server and web recipes

Break attributes/default.rb into multiple files because it got
sufficiently complex
Merge branch 'master' into refactor_default_recipe

Conflicts:
	attributes/default.rb
Merge pull request #7 from RiotGames/refactor_default_recipe

Refactors fuctionality from recipes/default.rb into recipes/common.rb