Add CHAP credentials support

Currently, the Hyper-V driver ignores the according CHAP
credentials when logging in iSCSI targets. For this reason,
attaching volumes fails when CHAP authentication is enforced.

This patch adds one way CHAP authentication support.

(cherry picked from commit 0309ba9480a6734f633241e9a5bd51bb8cacd0e1)

Change-Id: Id4d8800ae08dc24a01fc146f65c68b0b41d49e3d
Merge "Add CHAP credentials support" into stable/juno