testsuite: test Python KVS more thoroughly

Problem: In python/t0005-kvs.py, the set_and_check_context() function
uses the same KVSDir object to write and read a value back.  This doesn't
ensure that the KVS data was actually commited to the KVS successfully,
as the data may just be locally cached in the KVSDir object.

Solution: After performing a KVS commit, open a new KVSDir object to ensure
the data has been written to the KVS correctly.

Author: chu11

t/python/t0005-kvs.py

@@ -35,10 +35,13 @@ def set_and_check_context(self, key, value, type):
         kd = flux.kvs.KVSDir(self.f)
         kd[key] = value
         kd.commit()
-        nv = kd[key]
+
+        kd2 = flux.kvs.KVSDir(self.f)
+        nv = kd2[key]
         self.assertEqual(value, nv)
         self.assertTrue(isinstance(nv, type))
-        return kd
+
+        return kd2
 
     def test_set_int(self):
         self.set_and_check_context("int", 10, int)