Ensure the network is scheduled to an dhcp-agent

For some reason DHCP-agent is not present in neutron
agent-list output immediately after start, so we have
to wait a bit.

By the time we are going to schedule the neutron network
to the dhcp agent it might have already been scheduled,
so we should be able to handle this case too.

Partial-Bug: #1241042
Related-Bug: #1231366

Change-Id: Ib40183a21e6ca99fa46e5b94782535cad980eec2
Use neutron-dhcp-agent dhcp driver by default

We are now relying on neutron-dhcp-agent features
like host routes, so we must use neutron-dhcp-agent
in undercloud instead of bm-dnsmasq in order to
deploy overcloud properly.

Co-Authored-By: Derek Higgins <derekh@redhat.com>

Closes-Bug: #1241042

Change-Id: I71b5efa72eaddb3ec07eda25336f421393635c1a
Merge "Ensure the network is scheduled to an dhcp-agent"
Merge "Use neutron-dhcp-agent dhcp driver by default"