Add Exclude and Include Route for Path Computation

Add Exclude and Include Route for Path Computation

Exclude Route Object (XRO) and Include Route Object (IRO) are
part of RFC5440. Both objects have for goal to add constraints
on path computation: XRO to exclude some nodes or links and
IRO to force inclusion of them i.e. force some points for the
path description.

This new patch enhance the path-computation.yang model as well
as Path Computation algorithms to support both Exclude and
Include routes. If Exclude Route could be express without any
specific order, Include Route must be an ordered list of point:
i.e. to through A, then B and C, list should be <A, B, C> and
not <C, A, B> or other order.

Change-Id: I254086146ed03c8591d54bce3f7c527372ac9134
Signed-off-by: Olivier Dugeon <olivier.dugeon@orange.com>