autoinstall: add missing subnets to preseed.cfg

Subnets:
- labs-support1-b-codfw
- labs-hosts1-c-eqiad
- labs-hosts1-d-eqiad
...had a subnets/ cfg file but no preseed.cfg config to point there.

Change-Id: Ib0e0f232de73a7dbb9565efed97516266d4ede72