chardev: tcp: postpone TLS work until machine done

chardev: tcp: postpone TLS work until machine done

TLS handshake may create background GSource tasks, while we won't know
the correct GMainContext until the whole chardev (including frontend)
inited.  Let's postpone the initial TLS handshake until machine done.

For dynamically created tcp chardev, we don't postpone that by checking
the init_machine_done variable.

Signed-off-by: Daniel P. Berrange <[email protected]>
[peterx: add missing include line, do unit test]
Signed-off-by: Peter Xu <[email protected]>
Message-Id: <20180308140714[email protected]>
Acked-by: Paolo Bonzini <[email protected]>
Signed-off-by: Eric Blake <[email protected]>