Did some cleanup to stop us from leaking Pipe file descriptors.

The main issue was the Communication::Disconnect() was calling its Connection::Disconnect() but this wouldn't release the pipes that the ConnectionFileDescriptor was using. We also have someone that is holding a strong reference to the Process so that when you re-run, target replaces its m_process_sp, but it doesn't get destructed because someone has a strong reference to it. I need to track that down. But, even if we have a strong reference to the a process that is outstanding, we need to call Process::Finalize() to have it release as much of its resources as possible to avoid memory bloat. 

Removed the ProcessGDBRemote::SetExitStatus() override and replaced it with ProcessGDBRemote::DidExit().

Now we aren't leaking file descriptors and the stand alone test suite should run much better.

llvm-svn: 238089