Catch error if name of graph doesn't exist in brain bundle for plot_rich_club about scona

[Islast]

The code good to me Ruslan, however I feel a little anxious about using the term "Real Graph" in an error message as it's pretty ambiguous.

[wingedRuslan]

@KirstieJane thanks for noticing that. I will fix that

[wingedRuslan]

@KirstieJane I've added a message that explicitly explains the error.

Is that what you wanted?

    try:
        rc_real = np.array(rich_club_df[real_network])
    except KeyError:
        raise KeyError(
           "Please check the name of the Real Graph in GraphBundle. There is"
            " no graph keyed by name {}".format(real_network))

[Islast]

I think it's safe to close this issue, the real graph question is better discussed elsewhere