mdadm: Fix native --detail --export

mdadm: Fix native --detail --export

Mentioned commit (see Fixes) causes that UUID is not swapped as expected
for native superblock. Fix this problem.

For detail, we should avoid superblock calls, we can have information
about supertype from map, use that.

Simplify fname_from_uuid() by removing dependencies to metadata
handler, it is not needed. Decision is taken at compile time, expect
super1 but this function is not used by super1. Add warning about that.
Remove separator, it is always ':'.

Fixes: 60c19530dd7c ("Detail: remove duplicated code")
Signed-off-by: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>