Merge pull request #6784 from chainer-ci/bp-6781-v10-fix-prep-script

[backport] CI: Fix prep script to show build failure details

.pfnci/linux/main-flexci-prep.sh

@@ -8,6 +8,13 @@ env
 
 gcloud auth configure-docker
 
-for DF in "$(dirname ${0})"/tests/*.Dockerfile; do
-    echo "$(basename "${DF}")" | cut -d . -f 1
-done | xargs -i -n 1 -P 4 bash -c 'echo "flexci-prep: $2 start"; DOCKER_IMAGE_CACHE=0 "$1" "$2" build push rmi > /dev/null 2>&1 && echo "flexci-prep: $2 succeeded" || echo "flexci-prep: $2 failed"' -- "$(dirname ${0})/run.sh" "{}"
+for DF in $(find "$(dirname ${0})/tests" -name "*.Dockerfile" -type f); do
+    echo "$(basename "${DF}" .Dockerfile)"
+done | xargs -i -n 1 -P 4 bash -c '
+    echo "flexci-prep: $2 start";
+    DOCKER_IMAGE_CACHE=0 "$1" "$2" build push rmi > "log_$2.out" 2>&1 && (
+        echo "flexci-prep: $2 succeeded"
+    ) || (
+        echo "flexci-prep: $2 *** FAILED ***" && cat "log_$2.out" && echo "flexci-prep: terminating further builds" && exit 255
+    )
+    ' -- "$(dirname ${0})/run.sh" "{}"