Fix pool_full race condition

Sometimes the main thread starts before the spawned thread, which means
that the thread that is supposed to hold open a connection starts after
the main thread has already successfully made a connection. This means
that the test for a successful connection attempt[1] was nearly useless
since the main thread would get the connection first and activate it[2]
no matter how long the spawned thread waited, and the test for a failed
connection attempt[3] would intermittently fail since is sometimes able
to get the connection before the busy-waiting worker thread does.
Adding a short sleep in the main thread ensures that the main thread
yields to the worker thread and it can grab the connection first so we
can actually test what happens in the main thread.

[1] http://git.openstack.org/cgit/openstack/ldappool/tree/ldappool/tests/test_ldappool.py#n183
[2] http://git.openstack.org/cgit/openstack/ldappool/tree/ldappool/__init__.py#n167
[3] http://git.openstack.org/cgit/openstack/ldappool/tree/ldappool/tests/test_ldappool.py#n193

Change-Id: Ic32ef931cd672907dd14d5ec6339a6d7d9a2018d

ldappool/tests/test_ldappool.py

@@ -149,7 +149,6 @@ class TestLDAPSQLAuth(unittest.TestCase):
             cn = worker.results[0][0][1]['cn']
             self.assertEqual(cn, ['admin'])
 
-    @unittest.skip("race conditions make this fail the gate")
     def test_pool_full(self):
         dn = 'uid=adminuser,ou=logins,dc=mozilla'
         passwd = 'adminuser'
@@ -169,6 +168,7 @@ class TestLDAPSQLAuth(unittest.TestCase):
                     time.sleep(self.duration)
 
         def tryit():
+            time.sleep(0.1)
             with pool.connection() as conn:  # NOQA
                 pass