test: give osbuild time to clean up on SIGINT

When the test runner receives SIGINT, osbuild's mounts stay around.
osbuild handles SIGING correctly, but it doesn't have time before being
killed because it's parent went away.

Fix this by waiting on it explicitly in the test runner.

Fixes #119

test/osbuildtest.py

@@ -40,13 +40,22 @@ class TestCase(unittest.TestCase):
             osbuild_cmd.append("--build-pipeline")
             osbuild_cmd.append(build_pipeline)
 
+        p = subprocess.Popen(osbuild_cmd, encoding="utf-8", stdin=subprocess.PIPE, stdout=subprocess.PIPE)
+        if input:
+            p.stdin.write(input)
+            p.stdin.close()
         try:
-            r = subprocess.run(osbuild_cmd, encoding="utf-8", input=input, stdout=subprocess.PIPE, check=True)
-        except subprocess.CalledProcessError as e:
-            print(e.stdout)
-            raise e from None
+            r = p.wait()
+            if r != 0:
+                print(p.stdout.read())
+            self.assertEqual(r, 0)
+        except KeyboardInterrupt:
+            # explicitly wait again to let osbuild clean up
+            p.wait()
+            raise
 
-        result = json.loads(r.stdout)
+        result = json.load(p.stdout)
+        p.stdout.close()
         return result["tree_id"], result["output_id"]
 
     def run_tree_diff(self, tree1, tree2):