BUG-746: Added definition of vendor-specific tlv into pcep-types.
Added abstract vs-tlv parser.

Change-Id: I62f920f1db35161fe7fa37645f2a7318eaa434af
Signed-off-by: Milos Fabian <milfabia@cisco.com>
Signed-off-by: Robert Varga <rovarga@cisco.com>