VMAX driver - Change vendor_name from EMC to Dell EMC
VMAX driver - Change vendor_name from EMC to Dell EMC

Change vendor_name in common.py from EMC to Dell EMC to be
consistent with other Dell EMC drivers.

Change-Id: I9dc6145519af9de271002f1b028bb4e6853d0833
Closes-Bug: #1670723

eharney/cinder,Datera/cinder,j-griffith/cinder,phenoxim/cinder,openstack/cinder,mahak/cinder,j-griffith/cinder,eharney/cinder,openstack/cinder,phenoxim/cinder,Datera/cinder,mahak/cinder