[PDF] Switch to generate_config, unify templates

[PDF] Switch to generate_config, unify templates

- move bash template handling (previously expanded via `envsubst`)
  to lib.sh;
- move j2 template handling to lib.sh;
- move virsh network templates to 'mcp/scripts/virsh_net' subdir;
- switch virsh network templates from `envsubst` expansion to j2 and
  leverage generate_config.py, similar to PDF Fuel installer adapter;
- add relevant runtime env vars (e.g. SALT_MASTER, MAAS_IP) on the fly
  to PDF, to consume them in templates like params coming from PDF;
- parameterize virsh network definitions based on PDF (mgmt, public);

JIRA: FUEL-322

Change-Id: Ib94e78fc4f25797b9354a0552e884104da5d0003
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>