Fix remote test suite directory creation

r298203 make SBPlatform::MakeDirectory less recursive, which breaks the
test suite creation of test directory hierarchy creation on the remote
target. Since the function was never fully recursive, and the name does
not imply recursiveness, I fix the problem by modifying the test runner
to do the recursion manually.

I also make the runner complain more loudly when it fails to create the
directory -- previously it just printed the error to stdout and caused
most of the tests to hang, which is not very helpful in diagnosing the
problem.

llvm-svn: 298261