Adding tempest install to devstack

Stack.sh doesn't install tempest, but it would be useful if it did.

Change-Id: I2eba3738342cb4835a992aa1152939a8dc2f74da
diff --git a/samples/local.conf b/samples/local.conf
index 20c5892..9e0b540 100644
--- a/samples/local.conf
+++ b/samples/local.conf
@@ -93,3 +93,9 @@
 # moved by setting ``SWIFT_DATA_DIR``. The directory will be created
 # if it does not exist.
 SWIFT_DATA_DIR=$DEST/data
+
+# Tempest
+# -------
+
+# Install the tempest test suite
+enable_service tempest
\ No newline at end of file