Specify storage IP for iscsi connector

The virt drivers supply a connector hash to cinder volumes when
attaching. This used to basically default to CONF.my_ip. This patch
allows the host to have a separate config option in the case the block
traffic is on a separate network.

DocImpact: Adds my_block_storage_ip config option for block traffic going
over a separate network.
Closes-Bug: #1347025

Change-Id: I2bab7226376acd7da78e038a230bf65613547ba6
Merge "Specify storage IP for iscsi connector"