Fix bug in PCE picking wrong client port

Fix bug in PCE picking wrong client port

- Instead of systematically picking the first available client port
compatible with the service, pick the client port provided by the input
request parameters when specified.
- Update existing node validation to pick only endpoints with tail
- Fix a bug in otn intermediate switch functional test suite.
- Remove from tapi-connectivity impl few lines of strange code that
seems being wrong since it was replacing the client port-name specified
in the request by its associated network port-name, what was making
Ethernet service creation failing.

JIRA: TRNSPRTPCE-460
Signed-off-by: Gilles Thouenon <gilles.thouenon@orange.com>
Change-Id: Ic3f1203f62fa19db46935524200c47f74611187c