Modify integration tests to fail on panic

tests/fixture/failure/compFailure.rs

@@ -0,0 +1,3 @@
+fn main() {
+    let
+}

tests/fixture/failure/compNoExercise.rs

@@ -0,0 +1,2 @@
+fn main() {
+}

tests/fixture/failure/info.toml

@@ -0,0 +1,7 @@
+[[exercises]]
+path = "compFailure.rs"
+mode = "compile"
+
+[[exercises]]
+path = "testFailure.rs"
+mode = "test"

tests/fixture/failure/testFailure.rs

@@ -0,0 +1,4 @@
+#[test]
+fn passing() {
+    asset!(true);
+}