iRMC: Follow-up: volume boot for virtual media boot interface
iRMC: Follow-up: volume boot for virtual media boot interface

This patch fixes a bunch of issues in the patch for volume boot support
for iRMC virtual media boot interface:
  I387ae9382ebc561bc721dcfed6416b25f4809183

Change-Id: Ib26236a6b65ea56f7d72e45c5bf6e3f4e52a2694
Related-Bug: #1677436

openstack/ironic,pshchelo/ironic,openstack/ironic,pshchelo/ironic