[tests]: Specify versions of pip packages (#1227)

* [tests]: Specify versions of pip packages

* Update README.md

tests/README.md

@@ -14,7 +14,7 @@ SWSS, Redis, and all the other required components run inside a virtual switch D
     ```
     sudo modprobe team
     sudo apt install net-tools ethtool
-    sudo pip install docker pytest flaky redis
+    sudo pip install docker zipp==2.2.1 pytest==4.6.9 flaky redis
     ```
 3. Install `python-swsscommon_1.0.0_amd64.deb`. You will need to install all the dependencies as well in the following order:
 
@@ -106,4 +106,4 @@ For those developing new features for SWSS or the DVS framework, you might find
     ```
 
     You can mitigate this by editing the `DEFAULT_DOCKER_API_VERSION` in `/usr/local/lib/python2.7/dist-packages/docker/constants.py`, or by upgrading to a newer version of Docker CE. See [relevant GitHub discussion](https://github.com/drone/drone/issues/2048).
-    
+