Always install the homebrew version of Python. Fix #1437.

Otherwise, we sometimes end up using the system Python, for which we'd need to use sudo to install virtualenv. Brew complicates this by yelling at you if you do use sudo. So let's simplify things by always using the homebrew python, which is more up to date anyway.

letsencrypt-auto-source/letsencrypt-auto

@@ -359,8 +359,8 @@ BootstrapMac() {
       brew install dialog
   fi
 
-  if ! hash pip 2>/dev/null; then
+  if [ -z "$(brew list --versions python)" ]; then
-      echo "pip not installed.\nInstalling python from Homebrew..."
+      echo "python not installed.\nInstalling python from Homebrew..."
       brew install python
   fi
 

letsencrypt-auto-source/pieces/bootstrappers/mac.sh

@@ -14,8 +14,8 @@ BootstrapMac() {
       brew install dialog
   fi
 
-  if ! hash pip 2>/dev/null; then
+  if [ -z "$(brew list --versions python)" ]; then
-      echo "pip not installed.\nInstalling python from Homebrew..."
+      echo "python not installed.\nInstalling python from Homebrew..."
       brew install python
   fi