Add version test for Ceilometer cli

In the other cli tests, there are version tests. But only Ceilometer cli
test doesn't have it.
This commit adds the test.

Change-Id: I9ef89ad4f47127abe4e305541625ce5d27a7ad75
diff --git a/tempest/cli/simple_read_only/test_ceilometer.py b/tempest/cli/simple_read_only/test_ceilometer.py
index 7f2864f..8bdd633 100644
--- a/tempest/cli/simple_read_only/test_ceilometer.py
+++ b/tempest/cli/simple_read_only/test_ceilometer.py
@@ -49,3 +49,6 @@
 
     def test_ceilometermeter_alarm_list(self):
         self.ceilometer('alarm-list')
+
+    def test_ceilometer_version(self):
+        self.ceilometer('', flags='--version')