upload/koji: add support for GSSAPI/Kerberos auth

Prior this commit we only had support for username/password authentication
in the koji integration. This wasn't particularly useful because this
auth type isn't used in any production instance.

This commit adds the support for GSSAPI/Kerberos authentication.
The implementation uses kerby library which is very lightweight wrapper
around C gssapi library.

Also, the koji unit test and the run-koji-container script were modified
so the GSSAPI auth is fully tested.

krb5.conf

@@ -0,0 +1,7 @@
+include /etc/krb5.conf
+
+[realms]
+    LOCAL = {
+        kdc = localhost
+        admin_server = localhost
+    }