We currently disable the zfs module changes when we disable zfs
builds as part of cross-compilation.  We should disable the zfs
module checks whenever zfs itself is disabled.

Pull the zfs module disablement support such that it is always
present.

BugLink: http://bugs.launchpad.net/bugs/1737176Signed-off-by: Andy Whitcroft <apw@canonical.com>
Acked-by: Colin King <colin.king@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>