Only use dhcp if enable_dhcp is set on the network

Also removes an unused call to init_host if there is no network
to setup. The signature of this call was wrong so clearly it was
not being used.

Partially-implements blueprint better-support-for-multiple-networks

Change-Id: I33c86b1500f9a69081b4c6ecbe79151f10f69cea
Fix ImportError during docs generation

nova/openstack/common/db/sqlalchemy/test_migrations.py has an
explicit import for lockfile but lockfile is missing from
requirements.txt

Change-Id: I8ae62e5235d0348b9fcc30ef6269089930858aa6
Initialize Ironic virt driver directory

implements bp: add-ironic-driver

Change-Id: Iaee58de9c962d960688015efac95eb1a80cf1296
Merge "Fix ImportError during docs generation"
Merge "Initialize Ironic virt driver directory"
Merge "Only use dhcp if enable_dhcp is set on the network"