knotty: add code to support showing progress for sstate object querying

knotty: add code to support showing progress for sstate object querying

Add support code on the BitBake side to allow sstate.bbclass in
OpenEmbedded to report progress when it is checking for availability of
artifacts from shared state mirrors.

Part of the implementation for [YOCTO #5853].

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>