increase SBD timeout to 30 seconds

Vagrant environments can result in very sluggish VMs, especially when
low on memory.
rely purely on DHCP and preexisting box network config

The Crowbar client nodes must receive eth1 IPs from the admin node via
DHCP, so we don't want Vagrant to change eth1 to a different IP shortly
after during its provisioning phase, as that can open up nasty
heisenbugs resulting in e.g. a controller and a compute node with the
same IP.