Reduce detail about CloudFormation

This is an effort to reduce the number of API requests we're making,
to avoid being throttled (which is happening, and breaking Chef
runs when many cfn stacks are running).

If this fails, I'll add sleep+retry - which is really the correct
solution here.
Lock Berkshelf to v2
Restore details about the current cfn stack

These are used by recipe[elastera-env]...
Don't use the ohai cookbook to install the plugins.

It forces an additional reload of ohai every run, instead of just when
the plugins change.  Now, we never reload (so the plugins won't be
available until the next run).  This should be fine, as some version
of the plugin will be installed during the build of the base AMI.