Nova Ironic driver to set pxe_swap_mb in Ironic

This patch fix the Nova Ironic driver to make it look at the swap field
in the flavor and map it to Ironic as driver_info/pxe_swap_mb.

Change-Id: Ic6091fd6b6c8e1a32a33969ce5cdd20f6c243167
Closes-Bug: #1297937
Merge "Nova Ironic driver to set pxe_swap_mb in Ironic"