- Use xdist to speed up the testing that takes bit too much time

- specfile:
* remove two patched (included upstream):
- fix_numpy_1_17.patch
- fix_numpy_matrix_warning_test.patch
* add test requirement imageio
- update to version 0.16.2 (bsc#1157707):
* Bug fixes
+ Migrate to networkx 2.x (#4236, #4237)
+ Sync required numpy and dask to runtime versions (#4233, #4239)
+ Fix wrong argument parsing in structural_similarity (#4246,
#4247)
+ Fix active contour gallery example after change to rc
coordinates (#4257, #4262)
- changes from version 0.16.1:
* New Features
+ New `skimage.evaluate` module containing simple metrics (mse,
nrme, psd) and segmentation metrics (adapted rand error,
variation of information) (#4025)
+ n-dimensional TV-L1 optical flow algorithm for registration --
`skimage.registration.optical_flow_tvl1` (#3983)
+ Draw a line in an n-dimensional array -- `skimage.draw.line_nd`
(#2043)
+ 2D Farid & Simoncelli edge filters - `skimage.filters.farid`,
`skimage.filters.farid_h`, and `skimage.filters.farid_v` (#3775)
+ 2D majority voting filter assigning to each pixel the most
commonly occurring value within its neighborhood --
`skimage.filters.majority` (#3836, #3839)
+ Multi-level threshold "multi-Otsu" method, a thresholding