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/etc/tempest.conf.sample b/etc/tempest.conf.sample
index 3aa0497..ab65914 100644
--- a/etc/tempest.conf.sample
+++ b/etc/tempest.conf.sample
@@ -365,6 +365,8 @@
 enabled = True
 # directory where python client binaries are located
 cli_dir = /usr/local/bin
+# Number of seconds to wait on a CLI timeout
+timeout = 15
 
 [service_available]
 # Whether or not cinder is expected to be available