Zookeeper

This pull request addresses two issues:
* the metachef and silverware cookbooks both have a STANDARD_DIRS defined.  The silverware definition overrides the metachef def, but has :root instead of 'root' as the user for a number of directories.  The :root symbol isn't defined anywhere.  I changed silverware to match metachef, using 'root' instead for the user.
* the zookeeper cookbook doesn't define default attributes for data_dir and journal_dir.  This causes some strange behavior that I don't fully understand - the homedir for the zookeeper user is initially set to one thing, then in the next chef run, chef tries to change it to /mnt/somethingerother.  (sorry, I don't remember the values.)  This homedir change fails because the zookeeper process is already running.  Adding default values for those two variables results in the homedir for the user being set correctly the first time.