Storwize/SVC: Optional CHAP authentication

The Storwize/SVC driver doesn't work with Nova drivers that don't
support CHAP (e.g., HyperV). This patch makes CHAP optional.

DocImpact

Closes-Bug: #1224334
Change-Id: I22df4b916b2800a53c1e4968913f7e95965eaf4b
Merge "Storwize/SVC: Optional CHAP authentication"