Merge pull request #2451 from ipfs/t0300-improve-debug-message

t0300: improve docker_build debug message

test/sharness/t0300-docker-image.sh

@@ -33,7 +33,10 @@ TEST_TESTS_DIR=$(dirname "$TEST_SCRIPTS_DIR")
 APP_ROOT_DIR=$(dirname "$TEST_TESTS_DIR")
 
 test_expect_success "docker image build succeeds" '
-	docker_build "$TEST_TESTS_DIR/Dockerfile" "$APP_ROOT_DIR" >actual
+	docker_build "$TEST_TESTS_DIR/Dockerfile" "$APP_ROOT_DIR" >actual ||
+	test_fsh echo "TEST_TESTS_DIR: $TEST_TESTS_DIR" ||
+	test_fsh echo "APP_ROOT_DIR : $APP_ROOT_DIR" ||
+	test_fsh cat actual
 '
 
 test_expect_success "docker image build output looks good" '