src/test/kerberos and src/test/ldap try to run private authentication
servers, which of course might fail.  The logs from these servers
were being dropped into the tmp_check/ subdirectory, but they should
be put in tmp_check/log/, because the buildfarm will only capture
log files in that subdirectory.  Without the log output there's
little hope of diagnosing buildfarm failures related to these servers.

Backpatch to v11 where these test suites were added.

Discussion: https://postgr.es/m/16017.1565047605@sss.pgh.pa.us