Sync latest install_venv_common from oslo.

This commit syncs in the latest version of install_venv_common
from oslo, which fixes the import issue that was previously
addressed by change: I8a3df02a51c2c777d8f47cb8bc72d0644ae47095
which gets reverted by this commit.

Change-Id: I910610da5a4c413711819ca39627cb9ee94814ef

tools/install_venv.py

@@ -22,9 +22,6 @@
 import os
 import sys
 
-parentdir = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
-os.sys.path.insert(0, parentdir)
-
 import install_venv_common as install_venv
 
 

tools/install_venv_common.py

@@ -25,6 +25,13 @@ import os
 import subprocess
 import sys
 
+
+possible_topdir = os.getcwd()
+if os.path.exists(os.path.join(possible_topdir, "nova",
+                               "__init__.py")):
+    sys.path.insert(0, possible_topdir)
+
+
 from nova.openstack.common import cfg