MM-30708: Fix racy TestLdapConnect/STARTTLS_connection (#16448)

```release-note
NONE
```

https://mattermost.atlassian.net/browse/MM-30708

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

go.mod

@@ -67,7 +67,7 @@ require (
 	github.com/mattermost/go-i18n v1.11.0
 	github.com/mattermost/gorp v1.6.2-0.20200624165429-2595d5e54111
 	github.com/mattermost/gosaml2 v0.3.2
-	github.com/mattermost/ldap v0.0.0-20191128190019-9f62ba4b8d4d
+	github.com/mattermost/ldap v0.0.0-20201202150706-ee0e6284187d
 	github.com/mattermost/logr v1.0.13
 	github.com/mattermost/rsc v0.0.0-20160330161541-bbaefb05eaa0
 	github.com/mattn/go-colorable v0.1.8 // indirect