Use slot width granularity in PCE

Use slot width granularity in PCE

Adding a new constraint in spectrum assignment for path calculation:
slot width granularity from mc capabilities. If for node, slot width
granularity is equals to 50GHz then spectrum assignment will be done
in fixed mode.
- Add new method to PceNode interface and its implementation to get
 slot width granularity.
- Add new method to MappingUtils to get mc capabilities for a node.
- Update unit tests

JIRA: TRNSPRTPCE-230
Signed-off-by: manuedelf <emmanuelle.delfour@orange.com>
Change-Id: I84356d45c1b8652a05fee0ef66aa53b50b1de5b0