[DOC BLD FIX] Fix docstring problems in vzstorage driver
[DOC BLD FIX] Fix docstring problems in vzstorage driver

There are docstring issues in the vzstorage driver that
caused the Sphinx build process to produce WARNINGs.
This patch corrects those issues.

Change-Id: I0e009d4375ed029fe72c9e8728ec498b44683edb

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