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.sum

@@ -524,8 +524,8 @@ github.com/mattermost/gorp v1.6.2-0.20200624165429-2595d5e54111 h1:32+lDqjkY8hvc
 github.com/mattermost/gorp v1.6.2-0.20200624165429-2595d5e54111/go.mod h1:QCQ3U0M9T/BlAdjKFJo0I1oe/YAgbyjNdhU8bpOLafk=
 github.com/mattermost/gosaml2 v0.3.2 h1:kq2dY5qUe6fPPHra171GVlgo+ycBsEog0gZMetxL8ow=
 github.com/mattermost/gosaml2 v0.3.2/go.mod h1:Z429EIOiEi9kbq6yHoApfzlcXpa6dzRDc6pO+Vy2Ksk=
-github.com/mattermost/ldap v0.0.0-20191128190019-9f62ba4b8d4d h1:2DV7VIlEv6J5R5o6tUcb3ZMKJYeeZuWZL7Rv1m23TgQ=
-github.com/mattermost/ldap v0.0.0-20191128190019-9f62ba4b8d4d/go.mod h1:HLbgMEI5K131jpxGazJ97AxfPDt31osq36YS1oxFQPQ=
+github.com/mattermost/ldap v0.0.0-20201202150706-ee0e6284187d h1:/RJ/UV7M5c7L2TQ0KNm4yZxxFvC1nvRz/gY/Daa35aI=
+github.com/mattermost/ldap v0.0.0-20201202150706-ee0e6284187d/go.mod h1:HLbgMEI5K131jpxGazJ97AxfPDt31osq36YS1oxFQPQ=
 github.com/mattermost/logr v1.0.13 h1:6F/fM3csvH6Oy5sUpJuW7YyZSzZZAhJm5VcgKMxA2P8=
 github.com/mattermost/logr v1.0.13/go.mod h1:Mt4DPu1NXMe6JxPdwCC0XBoxXmN9eXOIRPoZarU2PXs=
 github.com/mattermost/rsc v0.0.0-20160330161541-bbaefb05eaa0 h1:G9tL6JXRBMzjuD1kkBtcnd42kUiT6QDwxfFYu7adM6o=