[baremetal] Move all MaaS PXE net config to PDF

[baremetal] Move all MaaS PXE net config to PDF

- s/opnfv_maas_pxe_/opnfv_infra_maas_pxe_/g to align with other vars;
- patches: pharos: Add MaaS PXE network to installer adapter;
- runtime.yml{,.template}: move to installer adapter, update
  pod_config.yml example;
- drop MAAS_PXE_NETWORK global env var, now read strictly from PDF;

JIRA: FUEL-313

Change-Id: I46d7510bd53fba7890c411d36bc28fd6ff6f3648
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
(cherry picked from commit 15e982f0d00dbcc72be2f5b25dab34b3f3efd912)