Enable the neutron dhcp and l3 agents

These need to be enabled in order for the upstart service to be allowed
to start, they are controlled by os-svc-enable-upstart as
OS_SVC_ENABLE_CONTROL is set in their upstart configs.

Change-Id: I20e2e4a672fcd124ba3e64ec9728d184c6ed0c22
Merge "Enable the neutron dhcp and l3 agents"