Make sure we are using an old version of pip on our dev machines.

Summary:
pip20+ stopped supporting python2.7.  We need to make sure we are
using an older pip.

Issue: https://khanacademy.slack.com/archives/C8Y4Q1E0J/p1613103475175600

Test Plan:
I ran
   if ! pip --version | grep -q "pip 1[0-9]"; then pip install -U "pip<20" setuptools; fi
manually in my shell twice.  The first time it successfully installed
something, the second time was a noop.

Reviewers: #devops, davidbraley

Reviewed By: #devops, davidbraley

Differential Revision: https://phabricator.khanacademy.org/D69259

shared-functions.sh

@@ -163,6 +163,12 @@ create_and_activate_virtualenv() {
 
     # Activate the virtualenv.
     . "$1/bin/activate"
+
+    # pip20+ stopped supporting python2.7, so we need to make sure
+    # we are using an older pip.
+    if ! pip --version | grep -q "pip 1[0-9]"; then
+        pip install -U "pip<20" setuptools
+    fi
 }
 
 # If we exit unexpectedly, log this warning.