Move filename from Install to create for Cache File

In order to support disabling the cache we need to have acces to the
filename earlier - so move it from the Install method to the Create
method.
Change file timestamp on Install

If we are installing files from the cache, then we want to make sure
that the timestamp gets updated - since Go really cares about the
timestamps.
Write file directly when cache disabled

When we disable the cache, then we should just write the files
directly.
More work on getting disabled cache mode working