handle OLM when spanloss > 28dB

handle OLM when spanloss > 28dB

- when calculated spanloss is out of OpenROADM range ( = ]0-28] dB),
  it is all the same set in the OTS interface.
- when the spanloss is greater than 28 dB ,
  the OLM servicePowerSetup fails and triggers the rollback of
  roadm-connection interfaces already configured by the renderer.
- Change OlmServiceStub to result value to success

NB: OpenROADM specifies that spanloss must be < 27 dB but there is 1 dB
of tolerance in the measurement accuracy.
Thus the supported range for spanloss = ]0,28] dB.

Change-Id: Ibae4357bde37ba78fc5bface060099f4bb7be0b6
JIRA: TRNSPRTPCE-90
Signed-off-by: Gilles Thouenon <gilles.thouenon@orange.com>
Co-authored-by: Christophe Betoule <christophe.betoule@orange.com>