Refactor to extract functionality from Sweetness

* Use ERB for server.conf
* Process list of UPSTREAM_SERVERS passed via ENV
* Ensure new SSL certificates each run

Fixes #11
Correctly remove temporary test key/certificate
Add FORCE_SSL option to automatically redirect all requests to HTTPS
Merge pull request #20 from fancyremarker/env-upstreams

Refactor as fully-functional reverse proxy
Add integration test for upstreams
Try to appease Quay
Adding HSTS header when FORCE_SSL is selected

The FORCE_SSL variable currently redirects any url from HTTP to HTTPS. This
patch adds the Strict-Transport-Security header in the response from HTTPS
requests, which makes any modern browser (except IE) remember that it should
always connect via HTTPS to any url on the same domain. This prevents SSL
stripping, where users are directed to click on an HTTP url and MITM'ed before
the server has a chance to upgrade to HTTPS.

The HSTS_MAX_AGE parameter can be used to configure the number of
seconds a browser remembers to always connect with HTTPS. The default is
one year.

I haven't included the "includeSubDomains" option for this header, since
that's probably too aggressive for a generic config like this. It can be
exposed as via a flag later if needed.
Merge pull request #21 from aaw/experimental

Adding HSTS header when FORCE_SSL is selected
Upgrade cipher list to more broadly enable PFS and mitigate POODLE on SSLv3
Add explicit tests for TLS_FALLBACK_SCSV support
Increase proxy_buffers to avoid upstream header issue in Firefox
Merge pull request #22 from fancyremarker/experimental

Increase proxy_buffers to avoid upstream header issue in Firefox
WebSockets support (fixes #18)
Merge pull request #23 from fancyremarker/experimental

WebSockets support
Resolve merge conflict
Merge pull request #27 from aptible/experimental

Merging experimental into master