IPA/AD: globally set krb5 canonicalization flag
If Kerberos principal canonicalization is configured in SSSD, currently
it is the default for the IPA provider, a configuration snippet is
generated for the system-wide libkrb5 configuration so that all
kerberized applications will use canonicalization by default.
Resolves https://fedorahosted.org/sssd/ticket/3041
Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>