Fixed #9893 -- Filename could exceed max_length on a collision

Passing max_length argument into the Storage's save() and get_available_name() methods.
Rewriting get_available_name() so filenames do not exceed max_length when there is a collision.
Adding test for the case.
`inspect.getargspec` is deprecated. Please use `inspect.getfullargspec` instead.

https://docs.python.org/3/library/inspect.html#inspect.getfullargspec