Spectrum assignment skipped the last node in path

Spectrum assignment skipped the last node in path

APIImpact

Corrects an issue were the last node in a path was not
taken into account during spectrum assignment.

A path consists of a list of source/destination node pairs,
eg [(N1,N2) (N2,N3) (N3,N4)].

Consider this network: [A] ----- [B],  were A and B are ROADMs.
During path computation the above example may produce a path
such as:
[(A-SRG1, A-DEG1) (A-DEG1, B-DEG1) (B-DEG1, B-SRG1)]

The bug caused the code to skip checking for available
spectrum on B-SRG1.

This was due to spectrum assignment is only processed
in the A-Z direction, combined with an iteration only
taking the source node into account.

JIRA: TRNSPRTPCE-772
Change-Id: Ia0822a1cdb0e4b5f67d9c9675e1203f0a0746ef6
Signed-off-by: Joakim Törnqvist <joakim.tornqvist@smartoptics.com>