improve error message for dataset upload

[mfeurer]

closes #920

Given the following piece of code:

import openml
import sklearn.datasets
import pandas as pd
import numpy as np

X, y = sklearn.datasets.make_classification()
data = pd.DataFrame(X)
data['y'] = y

my_dataset = openml.datasets.create_dataset(
    name="My cool dataset",
    description="foo",
    creator="bar",
    contributor=None,
    collection_date='01-01-2011',
    language='English',
    licence=None,
    default_target_attribute='label',
    row_id_attribute=None,
    ignore_attribute=None,
    citation="foo",
    attributes='auto',
    data=data,
    version_label='1.0',
)

the error message improves from

ValueError: Invalid symbols in name: My cool dataset

to

ValueError: Invalid symbols ' ' in name: My cool dataset

[PGijsbers]

Don't forget to update the unit tests.

[codecov-commenter]

Codecov Report

Merging #927 into develop will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop     #927      +/-   ##
===========================================
- Coverage    88.05%   88.05%   -0.01%     
===========================================
  Files           37       37              
  Lines         4363     4521     +158     
===========================================
+ Hits          3842     3981     +139     
- Misses         521      540      +19     

Impacted Files	Coverage Δ
openml/datasets/dataset.py	86.57% <100.00%> (+0.59%)	⬆️

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