This fix is long-overdue for fixing bnc#841788.
It is now (at last) safe as pam no longer build-requires libtirpc.

- Change BuildDepends from krb5-devel to krb5-mini-devel
for those releases which provide it
as the later is sufficient and has fewer down-stream
dependencies.
- Use krb5 rather than gssglue to provide gss
access routines.
Both krb5 and gssglue provide routines of the same
name, and both can get linked into rpc.gssd, resulting
in some confusion.
Upstream support seems to be leaning heavily towards
avoiding libgssglue. nfs-utils is built without it,
and best to build libtirpc without it.
(bnc#841788)