Update the device connection credentials in the backend.

Updates the credentials of the device. This can only be done if the cloudManagedCredentials boolean returned
in the GET API is false. This api comes in hand when the device credentials have changed, for instance via
device's web interface and you want to update the backend with the new credentials.
By default the new credentials will be tested before being saved. You can control this behaviour and avoid
the test by setting optional parameter 'skipValidation' to True.
If test of new credentials is performed and fails, no changes will be saved and the request will return a
validation error.