Fix for the deprecated library function
Fix for the deprecated library function

os.popen() is deprecated since version 2.6. Resolved with use of
subprocess module.

Change-Id: I53c21d6e8a9d23646c236ae33d652f1aefc20153
Closes-Bug: #1529836

klmitch/python-keystoneclient,klmitch/python-keystoneclient