Use first mech's status in gss_acquire_cred

If we can't acquire creds for any mech in gss_acquire_cred, return the
status of the first mech instead of the last mech, as it's more useful
in the typical case (where the first mech is krb5 and the last mech is
SPNEGO).  This error reporting is not ideal when the user was
expecting to use some mech other than krb5, but it's about as good as
things were prior to #6894.

https://github.com/krb5/krb5/commit/71ca96850348569a7358b32301bb0cc60eb08103
Author: Greg Hudson <ghudson@mit.edu>
Commit: 71ca96850348569a7358b32301bb0cc60eb08103
Branch: master
 src/lib/gssapi/mechglue/g_acquire_cred.c |   14 +++++++++++---
 1 files changed, 11 insertions(+), 3 deletions(-)