Fixed stdio redirection within LLDB to "do the right thing" in all cases.

The main issue was if you didn't specify all three (stdin/out/err), you would get file actions added to the launch that would always use the pseudo terminal. This is now fixed.

Also fixed the test suite test that handles IO to test redirecting things individually and all together and in other combinations to make sure we don't regress.

<rdar://problem/18638226>

llvm-svn: 219711