Move finalize_components_config from get_params to cmd_*.

This allows us to redirect its output in cmd_cron, so that the
"src component not installed, skipped" message will be treated
the same way as other output from freebsd-update cron: Sent
in an email to root (or other address specified) if there are
updates to install, and silenced otherwise.

PR: 202492
MFC After: 1 week
Differential Revision: https://reviews.freebsd.org/D26432