[baremetal] PDF-based network config

[baremetal] PDF-based network config

This change extends current PDF/IDF support with:
- dynamic interface / vlan definition;
- dynamic interface and/or bridge allocation of installer networks on
  top of interfaces (physical or vlans);

This allows us to drop hardcoded interface names and vlan / bridge
configuration in favor of a runtime determined model based on PDF/IDF.

For now, we duplicate common jinja variable definitions in each
template, but this will later be moved to a common include file.

JIRA: FUEL-275

Change-Id: Ia80a66dbdf898b0bd0a4fb99d069ce9ebe33fa65
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>