Remove install options from pip install

[aderixon]

Specifying prefix and install-lib options to pip messes up the Graphite install, resulting in dependencies and modules being installed in inappropriate places - hence the confusion over the correct location of local_settings.py and static files. Use the defaults (no idea how you're supposed to install Graphite in a non-standard location with pip - advice would appear to be "don't").

Remove the install-option arguments from the pip task.