[[FIX]] ServerError to be BC with node8

[jmendiara]

V8 shipped with node8 break our test and reported a this.name inside
a ServerError instantiation, resulting in setting the name for a
NotFoundError to something like NotFound.Error

This can break logs in userland so this can be considered an inherited
breaking change

More info

  1) Therror when using ServerError should have precreated classes for statusCodes:

      AssertionError: expected { Object (error, message) } to deeply equal { Object (error, message) }
      + expected - actual

       {
      -  "error": "NotFound.Error"
      +  "error": "NotFound"
         "message": "The user Sarah does not exists"
       }

      at Context.<anonymous> (test/therror.spec.js:584:37)

  2) Therror when using ServerError should hide information to the client:

      AssertionError: expected 'ServiceUnavailable.Error' to deeply equal 'ServiceUnavailable'
      + expected - actual

      -ServiceUnavailable.Error
      +ServiceUnavailable

      at Context.<anonymous> (test/therror.spec.js:603:30)

  3) Therror when using ServerError should set string as message for ServerError:

      AssertionError: expected 'ServiceUnavailable.Error' to deeply equal 'ServiceUnavailable'
      + expected - actual

      -ServiceUnavailable.Error
      +ServiceUnavailable

      at Context.<anonymous> (test/therror.spec.js:616:30)

  4) Therror when using ServerError should set string as cause for ServerError:

      AssertionError: expected 'ServiceUnavailable.Error' to deeply equal 'ServiceUnavailable'
      + expected - actual

      -ServiceUnavailable.Error
      +ServiceUnavailable

      at Context.<anonymous> (test/therror.spec.js:629:30)

  5) Therror when using ServerError should set Number as message for ServerError:

      AssertionError: expected 'ServiceUnavailable.Error' to deeply equal 'ServiceUnavailable'
      + expected - actual

      -ServiceUnavailable.Error
      +ServiceUnavailable

      at Context.<anonymous> (test/therror.spec.js:643:30)

  6) Therror when using ServerError should set Number as cause for ServerError:

      AssertionError: expected 'ServiceUnavailable.Error' to deeply equal 'ServiceUnavailable'
      + expected - actual

      -ServiceUnavailable.Error
      +ServiceUnavailable

      at Context.<anonymous> (test/therror.spec.js:656:30)

[coveralls]

Coverage decreased (-0.9%) to 95.652% when pulling 364be1e on fix/node8 into 5d4f733 on master.