I think we should allow --use-krb5-ccache="" to indicate usage of the default ccache...
This bug was referenced in samba master: 994e12e8f7a6b089342a32a6c3269048bfef1545 0ba9e5dacbb4e5bf94600e0a4a1cbd9f7a9c5d9e aff2932c420fd102c077063b8d1f66cdd8a777cb 2674df4cc0e124d74eb9d764c29a07c9c84b94d6
This bug was referenced in samba master: 1e5546748cd22c9e654ed066ab1d27aadec0d3d3 4723d695608e7737176e4f6eb407885a38989fc8 c7d3946659ff9ce167f68f3f052fae02a8907869 a85f1b6facd2b641f98dcea9b997a02d8f276882