Simplify pip installation script

scripts/bootstrap

@@ -6,15 +6,9 @@ cd $(dirname $0)/..
 apt-get update
 apt-get install -y arptables python-pip python-dev rsync libssl-dev libffi-dev uuid-runtime
 
-# Fix bug on overlay w/ Docker
-pip uninstall -y py pip virtualenv >/dev/null >/dev/null 2>&1 || true
-pip install --upgrade pip tox
-
-# Switch to pip installed pip...
-/usr/local/bin/pip install psutil
-/usr/local/bin/pip install subprocess32
-/usr/local/bin/pip install ndg-httpsclient
 
+curl https://bootstrap.pypa.io/get-pip.py | python
+pip install tox psutil subprocess32 ndg-httpsclient
 
 if [ ! -x "$(which nsenter)" ]; then
     TMP=$(mktemp -d)