fix ceph-daemon image missing dependencies.

This PS fix ceph mgr modules having failed dependency with
python six module in ceph-daemon image based on ubuntu_focal.

Before this fix, the module six could be found in
/usr/local/lib/python3.8/dist-packages, and this path is in python3
sys.path, but somehow, ceph mgr modules can not find
module six. Add '--ignore-installed' in pip3 install cmd can fix this.

Story: #2010697
Change-Id: I3d9b3454aa253543f29f6f3dfa6048241ae70900

ceph-daemon/Dockerfile.ubuntu_focal

@@ -52,7 +52,7 @@ RUN set -ex ;\
         lvm2 ;\
     curl -sSL https://bootstrap.pypa.io/pip/3.6/get-pip.py | python3 ;\
     pip3 --no-cache-dir install --upgrade --ignore-installed PyYAML ;\
-    pip3 --no-cache-dir install --upgrade \
+    pip3 --no-cache-dir install --upgrade --ignore-installed \
       six \
       python-openstackclient \
       python-swiftclient ;\