COLIBRI: EERs stitching code in setup must check SegR type

[juagargi]

In our COLIBRI service we forgot to add code in the end to end reservation setup to check for segment types when stitching.
Not all combinations of segments are valid when stitching. These are the allowed ones:

• up, core, down
• up, down
• core, down

Note that with these combinations, whenever a core segment appears, the stitching point must ensure that the EER will follow the direction of the reservation. I.e. a core SegR A->B cannot be used to stitch C->B->A at stitching point B

TODO:

• Check segment type before stitching.
• Ensure that the segments are followed only in the order of the reservation, at any AS during the EER setup (not only stitching).
• When stitching, and as a particular case of the above point, ensure that the next segment is followed in the direction of the reservation.