pkg_search: Change URLs and honor possible mirror settings

pkg_search: Change URLs and honor possible mirror settings

- Change the version variable to match latest changes on avalon (2.2 ->
  2.2.0)
- If the user uses $BINPKG_SITES or /etc/settings.conf (like with
  pkg_radd) try to download the summary file from a mirror first.  If
  that fails, fall back to default aka avalon

NOTE: If someone changes the directory layout on avalon, please update
the pkg_* tools in base as well.