Added support for nesting role files in subdirectories of the role/ directory.

I happen to organize a lot of my role files into sub directories.  Spice weasel didn't support this so I quickly threw together some code that will support this.  I've only really tested it for my environment but it seems to work just fine.  


Running: spiceweasel --dryrun spiceweasel/capacity_xlarge.yml 

where capacity_xlarge.yml is

cookbooks:
  aws:
  lvm:
  volumes:

roles:
 - ec2_m1_xlarge_rev0:


and ec2_m1_xlarge_rev0.rb is located in roles/vm/

the following is the output

knife cookbook upload aws
knife cookbook upload lvm
knife cookbook upload volumes
knife role from file roles/vm/ec2_m1_xlarge_rev0.rb