tests/image: fix the selector

Using wildcard in quotes doesn't trigger shell expansion, therefore this
commit moves the wildcard out of the quotes

schutzbot/run_image_tests.sh

@@ -19,9 +19,9 @@ test_divider () {
 
 # Get a list of test cases.
 get_test_cases () {
-    TEST_CASE_SELECTOR="${ID}_${VERSION_ID%.*}-${ARCH}*.json"
+    TEST_CASE_SELECTOR="${ID}_${VERSION_ID%.*}-${ARCH}"
     pushd $IMAGE_TEST_CASES_PATH > /dev/null
-        ls "$TEST_CASE_SELECTOR"
+        ls "$TEST_CASE_SELECTOR"*.json
     popd > /dev/null
 }