ENH+BF: skip two tests requiring mayavi, and include into SkipTest caught exception

[yarikoptic]

Now it should include msg why actually skipping, e.g.

SKIP: Test test_kit2fiff_model skipped, requires mayavi. Got exception (No module named pyface.tvtk_scene)

Closes #3645

[codecov-io]

Current coverage is 87.39% (diff: 100%)

Merging #3655 into master will increase coverage by <.01%

@@             master      #3655   diff @@
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  Files           343        343          
  Lines         60764      60765     +1   
  Methods           0          0          
  Messages          0          0          
  Branches       9301       9300     -1   
==========================================
+ Hits          53107      53108     +1   
  Misses         4903       4903          
  Partials       2754       2754          

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[agramfort]

@christianbrodbeck can you have a look?

I think it's redundant with your open PR.

thanks @yarikoptic for taking the time to investigate.

[christianbrodbeck]

Yes #3648 should take care of it eventually, except for the decorator modification.

[agramfort]

@christianbrodbeck I propose to merge @yarikoptic's PR and that you rebase.

ok for you?

[christianbrodbeck]

Yes we can do that

[christianbrodbeck]

Thanks @yarikoptic !