add rhel 7 e2e test
use a flavor that supports HVM

rhel-7 seems to be HVM-only
* Dscl user provider changes to support Mac 10.7, 10.8 & 10.9.
* Make the dscl user provider password handling idempotent.
* Refactor / modernize dscl user provider unit tests.
* Functional tests for dscl user provider.
Updates based on PR comments.
use ec2-user for rhel7 image
e2e test on rhel found a bug
Changelog information for user dscl provider updates.
Merge pull request #1800 from opscode/sersut/chef#1634

DSCL User Provider Rewrite
Merge pull request #1811 from opscode/lcg/rhel-7-e2e

add rhel 7 e2e test
Add information on using Test Kitchen for E2E testing.
Create and test cookbook on Ubuntu 12.04
Remove kitchen tests from spec/ directory, so tests can be run separately.
Add test instructions and contributing information.
Update for Ubuntu end-to-end tests.