Added common test helpers.  Rewriting test_compile to use this.  First test is complete.
Added does_not_contain method for TextFileAssertHelper.
Added back integration test for Nginx.
Added back test for HTTPD w/custom WEBDIR
Refactored common assertions into component specific helpers.
Added support for getting options
Refactored many of the common assertions into the helper classes.  Updated code to use those helpers.
Added back test for stand-alone PHP app.  This involved adding another assert helper.
Set PATH and PHPRC, so that commands run don't need full paths to binaries or config.
Moved BaseCompileApp into a common file.
Rewrote NewRelic tests using new testing improvements.
Used DownloadAssertHelper to simplify common helpers.
Updated Codizy tests to use new test helpers.
Added extension to load additional preprocess commands.  These run after all of the other preprocess commands, so the environment should be fully setup, and just before the application itself runs.  This is a good place to run database migrations and things of that nature.
Added extension to source the `.env` file after it's rewritten.  This
will make the environment variables in it available to commands running
after that. It also removes the need to rewrite the `.env` file because
it's now being sourced by the shell and so it can just evaluate
environment variables normally.
Upgraded build pack utils to #8e4a0db.
Updated ErrorHelper to work with build_pack_utils updates, which now stream output.
Added check to make sure output is not empty.
Updated service_environment for HHVM extension to use $ instead of @
Removed check for rewrite of .env file.  Switched checks to look for export of env variables.