Not all error messages being returned correctly

[SColson82]

In the POST, the only error message that I am receiving, regardless of the error issue is:
Failed to create L2VPN. Status code: 400: Request does not have a valid JSON or body is incomplete/incorrect

The following error messages are in the SPEC and don't appear to be supported:

• 201: L2VPN Service Created
• 400: Request does not have a valid JSON or body is incomplete/incorrect
• 410: Can't fulfill the strict QoS requirements
• 402: Request not compatible (For instance, when a L2VPN P2MP is requested but only L2VPN P2P is supported)
• 409: L2VPN Service already exists.
  ------------------------------------ To be addressed in next release.
• 401: Not Authorized
• 411: Scheduling not possible
• 422: Attribute not supported by the SDX-LC/OXPO

[congwang09]

This is mostly updated. Will address 401, 411 and 422 in later PR.