The libpod/define code should not import any large dependencies,
as it is intended to be structures and definitions only. It
included the libpod/driver package for information on the storage
driver, though, which brought in all of c/storage. Split the
driver package so that define has the struct, and thus does not
need to import Driver. And simplify the driver code while we're
at it.
Signed-off-by: Matthew Heon <mheon@redhat.com>
befd40b57d