Avoid overriding default ccache for ads operations.

Avoid overriding default ccache for ads operations.

Avoid overriding default ccache for ads operations.

Nowadays various samba components may need to use GSSAPI and a default cred
cache to perform their tasks.
This code was completely overriding the whole process default ccache name, thus
altering the current credentials and sometimes hijacking them (or getting
preemptively hijaked).

By using gss_krb5_import_cred we can instead use a private ccache (necessary
sometimes to use a different set of credentials fromt he default
cifs/fqdn@realm one, for example when contacting foreign DCs using trust
credentials) that does not affect the rest of the process.

For the kerberos versions which don't have gss_krb5_import_cred
we fallback to temp override of KRB5CCNAME and gss_acquire_cred.

Signed-off-by: Alexander Bokovoy <ab@samba.org>
Signed-off-by: Günther Deschner <gd@samba.org>
Autobuild-User(master): Alexander Bokovoy <ab@samba.org>
Autobuild-Date(master): Wed Sep 12 21:18:09 CEST 2012 on sn-devel-104