fix tempest path

the path for tempest tests are incorrect. this ends up breaking
magnum gate magnum already has tempest plugin support

Change-Id: Ie58d6c15b5640bef73662f6427f0b07886f1a859
diff --git a/ceilometer/tests/tempest/plugin.py b/ceilometer/tests/tempest/plugin.py
index c3a446c..077a3c2 100644
--- a/ceilometer/tests/tempest/plugin.py
+++ b/ceilometer/tests/tempest/plugin.py
@@ -15,16 +15,18 @@
 
 import os
 
-from ceilometer.tests.tempest import config as tempest_config
 from tempest import config
 from tempest.test_discover import plugins
 
+import ceilometer
+from ceilometer.tests.tempest import config as tempest_config
+
 
 class CeilometerTempestPlugin(plugins.TempestPlugin):
 
     def load_tests(self):
         base_path = os.path.split(os.path.dirname(
-            os.path.abspath(__file__)))[0]
+            os.path.abspath(ceilometer.__file__)))[0]
         test_dir = "ceilometer/tests/tempest"
         full_test_dir = os.path.join(base_path, test_dir)
         return full_test_dir, base_path