Adopt tempest plugin config namespace

As a transition strategy to running heat_integrationtests as a
tempest plugin, this change puts the test config values in the
"heat_plugin" section. This will allow for either test runner
to be used during the transition.

blueprint tempest-plugin-support

Change-Id: I2eab50be92c998aeb1ee98011908a9828a7efe6c
diff --git a/common/test.py b/common/test.py
index c864d3b..413e51f 100644
--- a/common/test.py
+++ b/common/test.py
@@ -73,7 +73,7 @@
     def setUp(self):
         super(HeatIntegrationTest, self).setUp()
 
-        self.conf = config.init_conf()
+        self.conf = config.init_conf().heat_plugin
 
         self.assertIsNotNone(self.conf.auth_url,
                              'No auth_url configured')
@@ -106,7 +106,7 @@
                              'No admin username configured')
         self.assertIsNotNone(self.conf.admin_password,
                              'No admin password configured')
-        conf = config.init_conf()
+        conf = config.init_conf().heat_plugin
         conf.username = self.conf.admin_username
         conf.password = self.conf.admin_password
         conf.tenant_name = self.conf.admin_tenant_name