The patch adds support of ldap auth method to pgproto. For ldap we
request user password in clear text using corresponding protocol
message. Afterwards password is passed to tarantool authenticate
method which handles ldap based auth.
Important: since password is transferred as clear text it is advised to setup ssl.
test: refactor ldap machinery, so it is available to other tests too
test: run ldap test in CI (setup glauth)
Previously we didnt run it because glauth was missing from our image.