Make CLI timeout tests configurable

Add an option for configuring the timeout used in the compute
and keystone CLI tests.

Closes-Bug: #1208846

Change-Id: Ia8f2fe528da7c6f294a1047d1d8b84239ce17adc
diff --git a/tempest/cli/simple_read_only/test_compute.py b/tempest/cli/simple_read_only/test_compute.py
index e60e238..4c7f604 100644
--- a/tempest/cli/simple_read_only/test_compute.py
+++ b/tempest/cli/simple_read_only/test_compute.py
@@ -176,7 +176,7 @@
         self.nova('list', flags='--debug')
 
     def test_admin_timeout(self):
-        self.nova('list', flags='--timeout 2')
+        self.nova('list', flags='--timeout %d' % CONF.cli.timeout)
 
     def test_admin_timing(self):
         self.nova('list', flags='--timing')