Reduce use of sudo in Pootle Fabric scripts

It should not be needed to run mysql or mysqldump
This also makes it easier to clean up database dumps in {dump,load}_db
Properly bogus example domain names
Cleanup/simplify file confirmation logic
Add support for passwordless MySQL operations
Document passwordless configuration and mysql_conf
Improve wording in fabric docs

Change 'DB' to 'database' in most places
Enhance fabric commands to include from-scratch deployment and migration

Adds new migratedb and setup_db commands and documents the process for
creating a new database from scratch using create_db and setup_db.

The setup_db command will currently fail due to the South problems, but
migratedb will work on existing databases.

The update_db command is modified to perform both updatedb and migrate.
Provide better error message when PYTHONPATH is unset

Previous stack trace was particularly unhelpful

[ci skip]
Fix dump_db not to fail when there is no local copy to overwrite