Changing the error message for create_source error calls
Changing version to 1.2.2
Simplifying create_prediction code and check origin resources
Cleaning after pep8 and pylint and some docs
Changing checks on create functions

The create functions first check that the origin resources are
finished a limited amount of times. If they aren't still ready
we let them be used as origin resources in the create call,
that will fail with the corresponding message.

We also update the resource_is_ready function to accept HTTP_ACCEPTED as
a correct code for finished resources.
Refactoring to compact the checking of origin resources in create