Fixes the regression introduced by #10211 where the masked array fill
value type was not properly converted by astype.

Closes #12070.

The TestMaskedArrayMethods.test_sort_flexible test was failing for for
the subarray checks on big endian systems. That was probably due to
subarrays being sorted as bytestrings. This fixes the test by simply
checking that the sort does not error rather than checking the result.

Closes #11716.

This change was introduced as part of #10232

Fixes #11112

BUG: Ensure __array_finalize__ cannot back-mangle shape

Fixes #11021

Further progress in isolating matrix in preparation of its
deprecation.  There is one place left with an explicit reference
to matrix (in MaskedArray.count), which is to be solved later.

That function is nose specific and has not worked since `__init__` files
were added to the tests directories.

Use standard pytest markers everywhere in the numpy tests. At this point
there should be no nose dependency. However, nose is required to test
the legacy decorators if so desired.

At this point, numpy test cannot be run in the way with runtests, rather
installed numpy can be tested with `pytest --pyargs numpy` as long as
that is not run from the repo. Run it from the tools directory or some
such.