Add TopologyNetconfNodes.py library

Add TopologyNetconfNodes.py library

Our current method of configuring netconf topology devices does not
really scale in terms of speed and memory footprint.

Add TopologyNetconfNodes.py, which provides a simple library to
configure and ascertain connection establishment in a scalable way --
from the perspective of RF, both actions are single keywords which do
not produce much in terms of output.

The configuration part relies on RFC8072 YANG Patch to introduce any
number of devices through a single request.

The keyword to await connection polls NETCONF topology for device status
and loops until the deadline passes or all requested devices are found
to have been connected.

// FIXME: pass down authentication

JIRA: INTTEST-125
Change-Id: I1661d84a6535abff45cbd346f54e996a4d757b33
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>
Signed-off-by: Tomas Cere <tomas.cere@pantheon.tech>