In tests for multiple cluster networks we configure 2nd
admin network interface on master node in order to
bootstrap slaves from non-default nodegroup. When we use
IP from default admin network for PXE nodes from 2nd
nodegroup fail to boot (due to new firewall NAT rules),
so changing boot host to IP from 2nd admin network.
Change-Id: Iee8d349877eb93bfe2627c54efd28c17f629db93
Closes-bug: #1448978