Added 'arch' to ironic nodes

The arch property is displayed in the discovered nodes table.  Nova
BareMetal nodes do not have this information, but we don't need to
check for the type of node in the table, as it is specifically for
Ironic discovered nodes.

Change-Id: I78c60a55196edc4c0bcb660e45609f1cc16975a9
Merge "Added 'arch' to ironic nodes"