Added default nsqd upstart limits

* Defaulted nofile to 64 bit Linux default of 8192
* Defaulted nproc to total # of cpus
* The ulimit cookbook is declared as a dependency, yet it is not used.
  Removed the ulimit cookbook as a dep, since upstart's ulimit stanza
  is used.
Don't set nofile and nproc if not defined

Lets just let nsqd fall through to the system defaults if we don't
specifically set it.
Merge pull request #4 from retr0h/retr0h/run-nsqd-upstart-defaults

Added default nsqd upstart limits