Fix Drupal installation

- packages required by Drupal moved to provisioning script
- Drupal installation script deletes drupal root folder and database (if they exist) and recreates everything from scratch

TODO:
- drupal migration code (D6 -> D7) requires drupal6 production database and files to be copied. Two simple scripts for syncing db dump and files (user avatars, app screenshots etc) need be created to be able to run migration, I'll create them soon but they are not required if not migrate content from production  
- Drupal bootstrap blocks theme installation has been removed from shell script, it should be added to the make file (https://github.com/datagovuk/dgu_d7/blob/master/dgu.make)