Fix test_fix_argument_yes by closing temp files

The test was randomly failing which could be caused by a race
condition - the temporary files which are created during the
test weren't closed properly which could result in a situation
when they are not yet created but the test is trying to load
them.

Closes-Bug: #1918316
Change-Id: I7a5bf8b1404dbf96955b2eb96fb1a5552760a114
diff --git a/tempest/tests/lib/cmd/test_check_uuid.py b/tempest/tests/lib/cmd/test_check_uuid.py
index a621a75..403de38 100644
--- a/tempest/tests/lib/cmd/test_check_uuid.py
+++ b/tempest/tests/lib/cmd/test_check_uuid.py
@@ -29,12 +29,13 @@
            "        pass"
 
     def create_tests_file(self, directory):
-        with open(directory + "/__init__.py", "w"):
-            pass
+        init_file = open(directory + "/__init__.py", "w")
+        init_file.close()
 
         tests_file = directory + "/tests.py"
         with open(tests_file, "w") as fake_file:
             fake_file.write(TestCLInterface.CODE)
+            fake_file.close()
 
         return tests_file