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 while still populating the dbversion table
in the database.

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 drops 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 dbversion 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)