src/update_handler: add info message about selected adaptive method
src/update_handler: add info message about selected adaptive method

This might be quite helpful for debugging if adaptive updates work or
not.

While at it, also align the corresponding error message to use the term
'method'.

Signed-off-by: Enrico Joerns <a2e5f936c390f36494e46e71bcfbe365bb1e8c49@pengutronix.de>

ejoerns/rauc,rauc/rauc,jluebbe/rauc,rauc/rauc,rauc/rauc,ejoerns/rauc,ejoerns/rauc,jluebbe/rauc,jluebbe/rauc