Replace deprecated library function os.popen() with subprocess
Replace deprecated library function os.popen() with subprocess

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

Change-Id: I4d0044c110c32f87ac0316a7e665e2bb9ea88813
Partial-Bug: #1529836

openstack/cinder,NetApp/cinder,j-griffith/cinder,eharney/cinder,Datera/cinder,dims/cinder,dims/cinder,j-griffith/cinder,cloudbase/cinder,mahak/cinder,Nexenta/cinder,bswartz/cinder,eharney/cinder,ge0rgi/cinder,cloudbase/cinder,bswartz/cinder,NetApp/cinder,Nexenta/cinder,Datera/cinder,Hybrid-Cloud/cinder,Hybrid-Cloud/cinder,openstack/cinder,phenoxim/cinder,mahak/cinder,phenoxim/cinder