[v9_16] Test "tkey-gssapi-credential" conditionally
If "tkey-gssapi-credential" is set in the configuration and GSSAPI support is not available, named will refuse to start. As the test system framework does not support starting named instances conditionally, ensure that "tkey-gssapi-credential" is only present in named.conf if GSSAPI support is available.
(cherry picked from commit 6feac68b)
Closes #2634 (closed)