Fixes #8141 - correct instructions for testing in rake file
fixes #8411 - check if interfaces fact exists
Fixes #8422 - primary detection for non-discovered

We injected discovery way to chose primary interface to puppet fact
parser that is used also for not discovered host which are missing
discovery specific facts. Mac for such value was evaluated to nil
which matched also macaddress_lo so lo was chosen as primary
interface.
Aligned README with Discovery 2.0
Include notes on deploying the updated default template
Update README.md, make pxelinux.cfg/default notes clearer
Fixes #6764 - dropped TCL image deps
refs #6764 - leftovers from TCL image deps
Fixes #6134 - Discovered hosts prefix can be configured