Fix awake AMT unit test

If test methods of awake AMT test case executed on the same process
with short time between executions tests fails. This patch adds
reset of AMT_AWAKE_CACHE to setUp() method.

Closes-bug: #1522789

Change-Id: I91c2e60bd2a3a1f97de3a7256e78815ddbbf8087

ironic/tests/unit/drivers/modules/amt/test_common.py

@@ -179,6 +179,7 @@ class AMTCommonClientTestCase(base.TestCase):
 class AwakeAMTInterfaceTestCase(db_base.DbTestCase):
     def setUp(self):
         super(AwakeAMTInterfaceTestCase, self).setUp()
+        amt_common.AMT_AWAKE_CACHE = {}
         self.info = INFO_DICT
         self.node = obj_utils.create_test_node(self.context,
                                                driver='fake_amt',