Allow users to explicitly forgo using a build cache

[djoyahoy]

Allow users to create an image that will never use caching.

[ShadowJonathan]

Duplicate of #409?

[djoyahoy]

@ShadowJonathan this issue is slightly different. For #409, that would allow users to clear the contents of an existing image cache, but continue to use the cache for future builds. This issue, however, would allow users to create an image that will never use a cache.