Make `swh db init` command work *properly* with the --dbname option

This allows to run the command swh db init --dname DBURI without giving a configuration file AND properly set the db version, which can be handy some times when testing.

Note that this may not work for all swh packages, when the postgresql backend for the given swh package needs more configuration entries than just the psql connection string.

This more or less drop support for "old style" db sql init scripts:

• the swh db init will still work for an 'old style' package (in which the sql init scripts do create dbversio table and initialize it) but will display an error message,
• the --initial-version option has been dropped, since this made sense only for old style packages,
• the test data 'cli_new' has been renamed as 'cli' (in place of the previous "old style" one)