coreos-base/update_engine: Make use of ue-rs download_sysext binary

This pulls in
flatcar/update_engine#34 to switch from bash
with curl and decode_payload to the ue-rs download_sysext binary.

Author: pothos

sdk_container/src/third_party/coreos-overlay/coreos-base/update_engine/update_engine-0.4.10-r19.ebuild renamed to sdk_container/src/third_party/coreos-overlay/coreos-base/update_engine/update_engine-0.4.10-r20.ebuild

@@ -8,7 +8,7 @@ CROS_WORKON_REPO="https://github.com"
 if [[ "${PV}" == 9999 ]]; then
 	KEYWORDS="~amd64 ~arm ~arm64 ~x86"
 else
-	CROS_WORKON_COMMIT="8fb11a4abfbf42941efdd73d06ee180bb26557f6" # flatcar-master
+	CROS_WORKON_COMMIT="c4a4c8ba04d70c04e7efe8cb0414627f9c6e8172" # TODO: flatcar-master
 	KEYWORDS="amd64 arm64"
 fi