[CI] Stop testing lower-constraints and fix py27 job

This patch disables the lower-constraints job as it started
failing and we agreed during the PTG to drop it anyway. [1]

For Train and below additionally blacklist bandit 1.6.3 as
it was improperly released as a universal wheel. [2]

[1] http://lists.openstack.org/pipermail/openstack-discuss/2020-October/018445.html
[2] https://github.com/PyCQA/bandit/issues/663

Change-Id: Icfedd16ef9aed84e9f9be939e832c35e0d735efe
Depends-On: https://review.opendev.org/c/openstack/kolla-ansible/+/766180
(cherry picked from commit bc0a41cd02)

.zuul.d/project.yaml

@@ -1,7 +1,6 @@
 ---
 - project:
     templates:
-      - openstack-lower-constraints-jobs
       - openstack-python-jobs
       - openstack-python36-jobs
       - openstack-python37-jobs

test-requirements.txt

@@ -1,7 +1,7 @@
 # The order of packages is significant, because pip processes them in the order
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
-bandit>=1.1.0 # Apache-2.0
+bandit!=1.6.3,>=1.1.0 # Apache-2.0
 bashate>=0.5.1 # Apache-2.0
 beautifulsoup4>=4.6.0 # MIT
 coverage!=4.4,>=4.0 # Apache-2.0