Currently, if dhcp mapping from a network is removed, it is reassigned
to the network. This is because of the Network Scheduler's schedule
function, which considers balancing the networks with the agents, whether
enable_dhcp is set on its subnets or not. It does not take into account
the network_auto_schedule config option. This is particularly disturbing
when considering backends which have their provide their own DHCP.
With this patch, if network_auto_schedule is set to False, networks wont
be automatically scheduled to DHCP Agents. If DHCP is to be mapped to a
network, it can be mapped using the CLI itself.
While it may seem that this change is breaking what is already working,
but as mentioned earlier, if there are network backends which provide DHCP
support themselves, they wont need the automatic mapping, which the term
"network_auto_schedule" actually stands for.
Closes-Bug: #1647421
Change-Id: If1a6a2a174d0f737415efa2abce518722316a77b
139b496ef9