[COOK-2829] Expose AWS credentials for ebs_raid LWRP as parameters

Updated the ebs_raid provider to expect AWS credentials as parameters
rather than reading from a data bag internally.
Removing unnecessary string interpolation.
Adding new ebs_raid AWS key parameters to README.
Merge branch 'master' of https://github.com/opscode-cookbooks/aws

Conflicts:
	providers/ebs_raid.rb
	resources/ebs_raid.rb
Merge pull request #2 from lancefrench/master

COOK-2829: expose AWS credentials for ebs_raid LWRP as parameters, Author: Lance French