Keystone moved from python-ldap to pyldap in the Newton release and
python-ldap now requires a version of pyasn1-modules that exceeds
the upper-constraint in Ocata, which breaks repo builds.
This patch removes python-ldap and adds pyldap in its place.
Closes-Bug: 1736241
Change-Id: I55f1fcd928c70eff3488af50d3dddb588082eb43
(cherry picked from commit ffc9c9b5e6)