[APFloat] Changed APFloat::isNormal => APFloat::isFiniteNonZero for all tests in unittests.

I forgot to to do this in r184356. The only references were in APFloatTest.cpp.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184366 91177308-0d34-0410-b5e6-96231b3b80d8