Problem:

  - If the user runs prepare-dev.py and interrupts after the syncing database has started, they will end up with no super user when re-run the commmand. This is because the reviewboard.db is already existed.

Fix:

  - The database reviewboard.db only created when site.sync_database is called. I put a try catch KeyBoardInterrupt around the whole if options.sync_db. After calling prepare-dev.py, if we interrupt before syncing database happens, the reviewboard.db hasn't created yet. If the user calls it again, the super user will be promted again. Therefore, we only need to put the try catch when the site.sync_database is called to prompt the user about rm reviewboard.db before re-run the command.

Manual test: Interrupt after Synchronizing database is called and checked that the warning is printed to commandline. If the interrupt happens before the database is created, no warning is printed which is expected.