update replace database script to just change instance pointer
update replace database script to just change instance pointer

Change the script to import the data into a new database and then point
the existing instance at the new database. The new database is called
the same as the old one with the date in yyyymmdd format appended.

For #516

openstate/popit,mysociety/popit,openstate/popit,mysociety/popit,Sinar/popit,openstate/popit,Sinar/popit,mysociety/popit,mysociety/popit,Sinar/popit,openstate/popit,mysociety/popit,Sinar/popit