Check of create_using type in __prep_create_using

[AlexanderVNikitin]

In this code part we make a conclusion of type based on having clear() method.

    try:
        create_using.clear()
    except:
        raise TypeError("Input graph is not a networkx graph type")

It can lead to some bugs in future.
It would be better to check up type with some other ways. For example, by inspect module.

What do you think about it?

[hagberg]

I usually advocate to remove the create_using() idiom here - #1393 etc.
But I don't have consensus on a replacement plan yet.

[hagberg]

continue at #1393