(maint) rename functions for clarity + consistency

Rename the three primary functions that return ring handlers to 'build-ring-handler'.
(SERVER-114) endpoint to flush environment cache

Add a new HTTP endpoint to the admin API, /v1/flush-environment-cache,
which tells the Puppet ruby code to invalidate all of its environment
caches.
(SERVER-114) make API more RESTful

Change the endpoint which flushes Puppet's environment cache to be more
RESTful.  Previously, it was a POST to /flush-environment-cache.  This
commit changes it to a DELETE to /environment-cache.
(SERVER-114) add comment about test coverage
(SERVER-114) specify puppet.conf used by test

This allows the test to pass when the default certname is not
'localhost'.
(SERVER-114) /environment-cache header handling

Make the implementation of /environment-cache tolerate an 'Accept: */*'
header in the request.
Merge pull request #294 from KevinCorcoran/SERVER-114/add-flush-env-cache

SERVER-114 - add endpoint to flush env cache
(SERVER-208) Improve error message for missing `puppet-admin` section

This commit improves the error message for a missing `puppet-admin`
section in the Trapperkeeper configuration at startup.