Add python_version function to functions-common

This makes it possible to list virtual site-package directories
without statically stating the python version, which is a bit ugly.

Change-Id: I3e7ac39eb43cdc4f656e0c90f3bfb23545722aef
diff --git a/lib/keystone b/lib/keystone
index 997bb14..0f369af 100644
--- a/lib/keystone
+++ b/lib/keystone
@@ -164,7 +164,7 @@
         keystone_auth_port=$KEYSTONE_AUTH_PORT_INT
     fi
     if [[ ${USE_VENV} = True ]]; then
-        venv_path="python-path=${PROJECT_VENV["keystone"]}/lib/python2.7/site-packages"
+        venv_path="python-path=${PROJECT_VENV["keystone"]}/lib/$(python_version)/site-packages"
     fi
 
     # copy proxy vhost and wsgi file
diff --git a/lib/nova b/lib/nova
index 6ac9da3..7d2145b 100644
--- a/lib/nova
+++ b/lib/nova
@@ -259,7 +259,7 @@
         nova_keyfile="SSLCertificateKeyFile $NOVA_SSL_KEY"
     fi
     if [[ ${USE_VENV} = True ]]; then
-        venv_path="python-path=${PROJECT_VENV["nova"]}/lib/python2.7/site-packages"
+        venv_path="python-path=${PROJECT_VENV["nova"]}/lib/$(python_version)/site-packages"
     fi
 
     # copy proxy vhost and wsgi helper files