Option to increase verbosity of refreshCdbJsonFiles

Generating the JSON and md5 files can take a while (up to 2 minutes on
the beta cluster) which leave people with little clues about what is
going on.

The patch adds an optional "--verbose" option to refreshCdbJsonFiles
which is passed to it whenever mw-update-l10n is invoked with --verbose.

Change-Id: I0cfd59f0fd1ab962522b9d3008631560433959a0