Remove generate_driver_list dependency on cur dir
Remove generate_driver_list dependency on cur dir

tools/generate_driver_list.py assumes that the current directory is
the Cinder root directory. If the script is run from a different
directory, it doesn't generate the driver info. This patch changes
the current directory to the root directory before calling the
utility functions to generate the driver list.

Closes-bug: #1604269
Change-Id: I35829003868531ccd76ee26e83e0b51067984a6a

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