On the stability of TAP tests for LDAP

Hi all,
(Peter Eisentraut in CC)

crake has just complained about a failure with the LDAP test suite:
https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=crake&dt=2019-07-19%2001%3A33%3A31

# Running: /usr/sbin/slapd -f
/home/bf/bfr/root/HEAD/pgsql.build/src/test/ldap/tmp_check/slapd.conf
  -h ldap://localhost:55306 ldaps://localhost:55307
# loading LDAP data
# Running: ldapadd -x -y
/home/bf/bfr/root/HEAD/pgsql.build/src/test/ldap/tmp_check/ldappassword
-f authdata.ldif
ldap_sasl_bind(SIMPLE): Can't contact LDAP server (-1)

And FWIW, when running a parallel check-world to make my laptop busy
enough, it is rather usual to face failures with this test, which is
annoying.  Shouldn't we have at least a number of retries with
intermediate sleeps for the commands run in 001_auth.pl?  As far as I
recall, I think that we can run into failures when calling ldapadd and
ldappasswd.

Thanks,
--
Michael