Sync venv scripts from oslo-incubator

Currently install_venv.py and with_venv.sh create virtual
environment in .venv directory and there is no way to specify
the virtual environment path explicitly.

This has been fixed in oslo-incubator.
This patch sync those virtual environment scripts from oslo-incubator.
Also make run_test.sh and run_tempest.sh scripts to use 'VENV' env variable.

Change-Id: I55311cff4dea1f6c5adaa2a6d51eeee2f6cc71ea
Closes-Bug: 1370086
diff --git a/openstack-common.conf b/openstack-common.conf
index 1920295..16ba6a7 100644
--- a/openstack-common.conf
+++ b/openstack-common.conf
@@ -3,6 +3,8 @@
 # The list of modules to copy from openstack-common
 module=install_venv_common
 module=versionutils
+module=with_venv
+module=install_venv
 
 # The base module to hold the copy of openstack.common
 base=tempest