[1] Improve unit test code coverage for fabric8-data-importer above 90%

[tisnik]

Acceptance criteria:

• code coverage for the fabric8-data-importer is higher than the specified threshold 90%
• reports available on https://fabric8-analytics.github.io/dashboard/dashboard.html

[tisnik]

Actual code coverage report:

Name                                      Stmts   Miss  Cover   Missing
-----------------------------------------------------------------------
src/__init__.py                               2      0   100%
src/config.py                                22      0   100%
src/data_importer.py                        195     32    84%   86, 97, 120-131, 158, 177-178, 215-217, 264-266, 274-275, 282-295, 307, 312, 317, 322, 327, 343, 348, 353
src/data_source/__init__.py                   0      0   100%
src/data_source/abstract_data_source.py       6      0   100%
src/data_source/s3_data_source.py            36      2    94%   29-31
src/graph_manager.py                         38      0   100%
src/graph_populator.py                      176      1    99%   385
src/rest_api.py                              97     15    85%   35-39, 97, 100-102, 113-115, 124, 155, 161
-----------------------------------------------------------------------
TOTAL                                       572     50    91%

this is clearly higher that the specified threshold :)

[tisnik]

Releated PRs:

fabric8-analytics/fabric8-analytics-data-model#145
fabric8-analytics/fabric8-analytics-data-model#144
fabric8-analytics/fabric8-analytics-data-model#141
fabric8-analytics/fabric8-analytics-data-model#139
fabric8-analytics/fabric8-analytics-data-model#138
fabric8-analytics/fabric8-analytics-data-model#137
fabric8-analytics/fabric8-analytics-data-model#136
fabric8-analytics/fabric8-analytics-data-model#135