Add ldappool constraints to global pins

In order to be able to bind to LDAP with TLS we need version 2.1.0 of ldappool.

manual backport of : https://review.openstack.org/#/c/468416
Closes-Bug: #1693793

Change-Id: I7ccd06b4fc39660a7ff947f5d5f566069619d99b

global-requirement-pins.txt

@@ -6,6 +6,12 @@
 # Use this file with caution!
 #
 
+# Due to https://bugs.launchpad.net/openstack-ansible/+bug/1693793,
+# ldappool must be pinned to == 2.1.0.
+# https://review.openstack.org/#/c/468508/
+# TODO: mgariepy, remove this once upstream is fixed.
+ldappool==2.1.0
+
 # Due to https://bugs.launchpad.net/ceilometer/+bug/1660800, gnocchiclient
 # must be pinned to < 3.0.0. This constraint matches what is defined in
 # the optional dependencies specified here:

releasenotes/notes/ldappool-e79455337a02b05d.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - The version 2.1.0 of ldappool fix the issue with TLS bind on ldapserver.
+    It is set in global pin to fix the issue in OSA until the fix is made
+    upstream.