Fix inaccurate internet available report

When starting cloud, Pat would report unable to validate credentials
instead of the root problem that internet unavailable.  Switching to
VagrantProvider for this check avoids the problem, and indicates a bug
in AWSProvider that inaccurately reports that the internet is available
when it is not.
Merge branch 'PAT-EC2' of https://github.com/NREL/OpenStudio into PAT-EC2