Failed to discovery when iscsi multipath and CHAP both enabled

Failed to discovery when iscsi multipath and CHAP both enabled

Storage server may be configured to protect target discovering phase with CHAP
authentication, in this case existing discovery command will be failed in Nova
when iscsi multipath enabled. Nova need these below discovery auth properties.
    "discovery.sendtargets.auth.authmethod",
    "discovery.sendtargets.auth.username",
    "discovery.sendtargets.auth.password"

Cinder Storage driver need to send discovery auth properties to Nova in this
case and the properties are:
   iscsi_properties['discovery_auth_method']
   iscsi_properties['discovery_auth_username']
   iscsi_properties['discovery_auth_password']

This issue not just for IBM Storwize, but also other storage drivers who need
CHAP authentication to do iscsi discover.
The according nova change: https://review.openstack.org/#/c/148516/

Closes-Bug: #1367189

Change-Id: Ib528eed3a9fd5006c1649ef42233e1f943c38ab6