download/mrc: stricter error handling

the cbfstool command within subshell now also
exits with non-zero status, if it fails (most
likely because extraction failed, for some reason,
of the coreboot rom image for running through it)

resources/scripts/download/mrc

@@ -51,8 +51,8 @@ main()
 	printf "Downloading Intel MRC blobs\n"
 
 	check_existing && exit 0
-	build_dependencies
-	fetch_mrc
+	build_dependencies || fail "could not build dependencies"
+	fetch_mrc || fail "could not fetch mrc.bin"
 }
 
 check_existing()
@@ -74,16 +74,17 @@ check_existing()
 build_dependencies()
 {
 	if [ ! -d "${cbdir}/" ]; then
-	    ./download coreboot default
+	    ./download coreboot default || return 1
 	fi
 	if [ ! -f "${cbfstool}" ]; then
-	    ./build module cbutils default
+	    ./build module cbutils default || return 1
 	fi
+	return 0
 }
 
 fetch_mrc()
 {
-	mkdir -p mrc/haswell/
+	mkdir -p mrc/haswell/ || return 1
 
 	(
 	cd mrc/haswell/
@@ -102,22 +103,25 @@ fetch_mrc()
 	extract_coreboot chromeos-firmwareupdate-${_board}
 
 	../../${cbfstool} coreboot-*.bin extract -f mrc.bin \
-			-n mrc.bin -r RO_SECTION
+			-n mrc.bin -r RO_SECTION \
+					|| fail "Could not fetch mrc.bin"
 	rm -f "chromeos-firmwareupdate-${_board}" coreboot-*.bin \
 			"${_file}" "root-a.ext2"
 
 	printf "\n\nmrc.bin saved to ${_mrc_complete}\n\n"
 	)
+
+	return 0
 }
 
 download_image()
 {
-	_url=${1}
+	url=${1}
 	_file=${2}
 	_sha1sum=${3}
 
 	echo "Downloading recovery image"
-	curl "$_url" > "$_file.zip"
+	curl "$url" > "$_file.zip"
 	if [ "$(sha1sum ${_file}.zip | awk '{print $1}')" = "${_sha1sum}" ]
 	then
 		unzip -q "${_file}.zip"