Add lazy engine with style preprocessors.

[rwjblue]

Demonstrates an issue in ember-engines build pipeline.

Build failed.
File: /Users/rjackson/src/open-source/engine-testing/tmp/sass_compiler-input_base_path-QgL1m6Fg.tmp/addon.scss (1)
The Broccoli Plugin: [SassCompiler] failed with:
Error: File to import not found or unreadable: vanilla-addon-in-lazy-with-style-preprocessor.
Parent style sheet: /Users/rjackson/src/open-source/engine-testing/tmp/sass_compiler-input_base_path-QgL1m6Fg.tmp/addon.scss
    at options.error (/Users/rjackson/src/open-source/engine-testing/node_modules/node-sass/lib/index.js:291:26)

The broccoli plugin was instantiated at:
    at SassCompiler.Plugin (/Users/rjackson/src/open-source/engine-testing/node_modules/broccoli-plugin/index.js:7:31)
    at SassCompiler.CachingWriter [as constructor] (/Users/rjackson/src/open-source/engine-testing/node_modules/broccoli-sass-source-maps/node_modules/broccoli-caching-writer/index.js:18:10)
    at new SassCompiler (/Users/rjackson/src/open-source/engine-testing/node_modules/broccoli-sass-source-maps/index.js:20:17)
    at /Users/rjackson/src/open-source/engine-testing/node_modules/ember-cli-sass/index.js:38:12
    at Array.map (native)
    at SASSPlugin.toTree (/Users/rjackson/src/open-source/engine-testing/node_modules/ember-cli-sass/index.js:35:34)
    at /Users/rjackson/src/open-source/engine-testing/node_modules/ember-cli-preprocess-registry/preprocessors.js:180:26
    at Array.forEach (native)
    at processPlugins (/Users/rjackson/src/open-source/engine-testing/node_modules/ember-cli-preprocess-registry/preprocessors.js:178:11)
    at module.exports.preprocessCss (/Users/rjackson/src/open-source/engine-testing/node_modules/ember-cli-preprocess-registry/preprocessors.js:148:10)