(PUP-3624) Log at least at info level when --verbose is specified

The change for PUP-2998 means if you have `log_level=debug` in your
puppet.conf, then `puppet agent --test` will reduce the log level to info,
because `--test` implies `--verbose`.

This commit changes the semantics of `--verbose` (and `--test` agent) so
that we log *at least* at that level, but we won't downgrade.  This
affects all Puppet::Applications, e.g. puppet apply, agent, etc.

Note this wasn't an issue before PUP-2998 was implemented, because
log_levels could only be specified on the command line.