kpatch: allow kpatch load/unload/info for files

A user may want to load a module without having to install it to the
initrd.  In fact, 99% of the time I think that will be the typical usage
of "kpatch load", with a given file as an argument rather than a DB
module.

Have "kpatch load" and other commands take a file as input.  If the file
is not found, then check the DB.