EMC: Fix minor issue in VNX driver and unit tests

There were some minor issues in initial commit of VNX Direct Driver
Juno Update (https://review.openstack.org/#/c/104413/), such as typo,
unclear config option help message and missing period.

This change fix these issues.

Change-Id: I82bac9695c8138cff858013b3affeb0557dfcc02
Closes-Bug: #1354272
Merge "EMC: Fix minor issue in VNX driver and unit tests"