Pin docker.py to <7

Docker 7.0.0 introduced a pre build check for tag regex, which
fails where registry has port number defined - see [1] and [2].

[1]: a9b5494fd0
[2]: https://github.com/docker/docker-py/issues/3195

Also removing requirements check in CI as it is not allowing
such pinning, as kolla is not designed to be installed with
other openstack services in the same virtualenv.

Change-Id: Id64186bf87300f23acde4f90474abcd6944e5be0

.zuul.d/project.yaml

@@ -4,7 +4,6 @@
       - openstack-python3-jobs
       - openstack-python3-jobs-arm64
       - openstack-cover-jobs
-      - check-requirements
       - publish-openstack-docs-pti
       - release-notes-jobs-python3
       - periodic-stable-jobs

requirements.txt

@@ -1,5 +1,5 @@
 pbr!=2.1.0,>=2.0.0 # Apache-2.0
-docker>=3.0.0 # Apache-2.0
+docker>=3.0.0,<7.0.0 # Apache-2.0
 Jinja2>=3.0.1 # BSD License (3 clause)
 GitPython>=1.0.1 # BSD License (3 clause)
 oslo.config>=5.1.0 # Apache-2.0