fix: [docker-host] pin python ``docker`` package.

precise/host/hooks/install.d/70-0k.sh

@@ -209,6 +209,10 @@ else
     fi
 
     . /opt/venv/docker-compose/bin/activate
+    ## XXXvlab: docker version 3.5.0 is bugged on its requirement list:
+    ## error: Setup script exited with error in docker setup command: 'tests_require' must be a string or list of strings containing valid project/version requirement specifiers; Expected ',' or end-of-list in pytest==2.9.1; python_version == '3.3' at ; python_version == '3.3'
+
+    pip install docker==3.4.1
 
     ( cd /opt/apps/docker-compose &&
             python setup.py install )