Cleanup some test methods & test/sndarray_test.py

[e1000]

Hello,

here some first cleanup branch on tests :

• replace all occurences of failIf with assertFalse
• replace some deprecated failUnlessEqual with standard assertEqual
• rm obsolete if not arraytype ... in test/sndarray_test.py & rm a test on import

I first fancied, I could cleanup all tests methods, but that would be way to noisy.
2 tests of gfxdraw_test.py fail, they fail also on master, right ?

Once merged, we can check the test/sndarray_test.py in #496

[illume]

Thanks @e1000

Yeah, those are disabled so that the tests can pass on the CI.