RESTFul API: Error handling mechanism

Define error response format
Improve error messages with additional diagnostic information

MagnetoDB can have very wide set of error classes.

One option to support large set of errors is to extend our classes from oslo common.exceptions

Response body can be like this (this is body from Heat):

{
    "explanation": "The server could not comply with the request since it is either malformed or otherwise incorrect."
    "code": 400
    "error":
       {
          "message": "Table 'testtempest1686253921' already exists",
          "traceback": None,
          "type": "TableAlreadyExistsException"
      }
}