test/update_handler: test for returning hook install handler
test/update_handler: test for returning hook install handler

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

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