Allow Vulcanize options to be customized

[JohnRiv]

Since this tool would be used to execute Vulcanize instead of running Vulcanize directly, ideally it should allow users to customize the options passed to Vulcanize. Right now it's setting its own options without allowing an override.

Some of Vulcanize's options may only have one value that makes sense in this context, but at the least, I'd like to be able to be able to turn Vulcanize's --strip-comments option on when running web-component-shards.