Optionally install tempest and disable by default

In I78d51f04ed01da4ce8aa0e127be028f969d3b4f8 we turned off installing
tempest because we install it on stable branches where the stable reqs
do not equal the tempest master (branchless) reqs.

Leave this off by default since that is the behaviour we have in the
gate, and make default devstack as similar to the gate as possible. But
add an option to install tempest by default so developers can opt and
reproduce the previous behaviour.

Update the tempest section of the README with how to run tempest tests
and how to install tempest if desired.

Change-Id: Ie4ea7335a57917244873ec54658ca269ab765ce1

README.md

@@ -282,7 +282,15 @@ If tempest has been successfully configured, a basic set of smoke
 tests can be run as follows:
 
     $ cd /opt/stack/tempest
-    $ nosetests tempest/scenario/test_network_basic_ops.py
+    $ tox -efull  tempest.scenario.test_network_basic_ops
+
+By default tempest is downloaded and the config file is generated, but the
+tempest package is not installed in the system's global site-packages (the
+package install includes installing dependences). So tempest won't run
+outside of tox. If you would like to install it add the following to your
+``localrc`` section:
+
+    INSTALL_TEMPEST=True
 
 # DevStack on Xenserver
 

lib/tempest

@@ -63,6 +63,12 @@ BUILD_INTERVAL=1
 BUILD_TIMEOUT=${BUILD_TIMEOUT:-196}
 
 
+# This must be False on stable branches, as master tempest
+# deps do not match stable branch deps. Set this to True to
+# have tempest installed in devstack by default.
+INSTALL_TEMPEST=${INSTALL_TEMPEST:-"False"}
+
+
 BOTO_MATERIALS_PATH="$FILES/images/s3-materials/cirros-${CIRROS_VERSION}"
 BOTO_CONF=/etc/boto.cfg
 
@@ -94,8 +100,12 @@ function remove_disabled_extensions {
 
 # configure_tempest() - Set config files, create data dirs, etc
 function configure_tempest {
+    if [[ "$INSTALL_TEMPEST" == "True" ]]; then
+        setup_develop $TEMPEST_DIR
+    else
         # install testr since its used to process tempest logs
         pip_install $(get_from_global_requirements testrepository)
+    fi
 
     local image_lines
     local images