Add vmedia boot support for deploy-ironic element

deploy-ironic element currently retrieves token over tftp and
expects BOOT_IP_ADDRESS to be set.  This commit adds support for
retrieving token file from virtual media if node booted from
virtual media. Also corrects the issue for BOOT_IP_ADDRESS not set
for virtual media boot.

Change-Id: I3d5f1779b9b17842360860c7778baa01db1e1a52
Closes-Bug: #1356339
Merge "Add vmedia boot support for deploy-ironic element"