Vagrant: Run pip install from $PROJECT_DIR

Makes it easy to install submodules and packages that are checked in to git

vagrant/provision.sh

@@ -22,7 +22,7 @@ su - $DEV_USER -c "echo $PROJECT_DIR > $VIRTUALENV_DIR/.project"
 su - $DEV_USER -c "$PIP install --upgrade pip"
 
 # Install PIP requirements
-su - $DEV_USER -c "$PIP install -r $PROJECT_DIR/requirements/base.txt"
+su - $DEV_USER -c "cd $PROJECT_DIR && $PIP install -r requirements/base.txt"
 
 
 # Set execute permissions on manage.py as they get lost if we build from a zip file