specify EC2 tags in the minion profiles

[rubic]

We should have the ability to specify EC2 tags in the minion profile as a yaml dict of key/value pairs. Shaker currently makes an implicit assignment to the Name tag based on the hostname value (if the hostname isn't already assigned as a tag).

@roncohen raises an interesting point in issue #13 of how EC2 tags may relate to grain roles. There may often be some overlap but I don't think Shaker should implicitly conflate tags into roles. However, I would have no problem with adding a tags attribute to grains.

grains:
    tags:
      key1: value1
      key2: value2