Hang when child process exits without writing to IPC pipe

[rainersigwald]

After MSBuild starts a child/worker process, it tries to handshake with the newly-created node by writing to an IPC pipe and waiting for the handshake response.

If process creation fails, an error is propagated upward and MSBuild doesn't hang. If, however, process creation succeeds but the child quickly terminates instead of waiting for the handshake, the indefinite blocking read on handshake response turns into a mysterious MSBuild hang.

We should either have a timeout for handshake success, or at the very least fail early in WaitForConnectionFromProcess if the nodeProcessId doesn't belong to a running process.