fix: Point to compatible pip for Python 2.7

On our CI images, the `python` executable is Python 2.7.

pip 21.0 dropped support for Python 2.7 (pypa/pip#9500)
and says to use a different URL to still retain that support. In order to install AWS CLI
from pip, we need to have a compatible version of pip.

circleci/utils

@@ -16,7 +16,10 @@ install_awscli(){
 
   echo "Installing AWS cli..."
   rm -rf ~/.local
-  wget --directory-prefix=/tmp/ https://bootstrap.pypa.io/get-pip.py
+
+  # Download the versioned pip installer which works with Python 2.7 (https://github.com/pypa/pip/issues/9500)
+  # TODO: Replace in favor of installing AWS CLI v2 directly
+  wget --directory-prefix=/tmp/ https://bootstrap.pypa.io/2.7/get-pip.py
   sudo python /tmp/get-pip.py
 
   sudo apt-get update