str.replace() is not the same as str.translate()

If we want to remove both : and -, then we can futz around with translate
or we can just call replace() twice.

Signed-off-by: Andy Grover <agrover@redhat.com>
Fix fcoe from_fabric_wwn

Add comment for from_fabric_wwn to attempt to explain where all the
issues are coming from.

from_fabric_wwn is to convert tcm_fc wwn format to canonical. What's in
/sys/class/fc_host/.. is a different format and should be converted
to canonical separately.

Signed-off-by: Andy Grover <agrover@redhat.com>