[FIX] Minor errors after migration to setuptools

[oesteban]

• Fixes nipype nosetests documentation broken #1670
• Make sure matplotlib default backend is Agg in docker images
• Do not use nipype.testing.assert_equal in nipype.interfaces.utility
• update new fsl_course_data link in docs

[oesteban]

I am also going to use OSF for hosting the test data files, since google drive is shutting down the api for direct downloads.

See: https://circleci.com/gh/nipy/nipype/1545

[codecov-io]

Current coverage is 70.95% (diff: 0.00%)

Merging #1671 into master will increase coverage by 6.58%

@@             master      #1671   diff @@
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  Files           232       1028     +796   
  Lines         36051      51607   +15556   
  Methods           0          0            
  Messages          0          0            
  Branches       4340       7315    +2975   
==========================================
+ Hits          23207      36618   +13411   
- Misses        12406      13900    +1494   
- Partials        438       1089     +651   

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[oesteban]

@satra - please check these little changes and merge if ok

[satra]

@oesteban - we should update the test command in the install docs as well. i can merge it right after that change since i know the tests pass. next up will be fixing doc building on readthedocs. we may need two separate requirements files.

[oesteban]

@satra - I updated the makefile so that it runs the appropriate test command and also updated the documentation.