char: ensure all clients are in non-blocking mode

Only some callers of tcp_chr_new_client are putting the
socket client into non-blocking mode. Move the call to
qio_channel_set_blocking() into the tcp_chr_new_client
method to guarantee that all code paths set non-blocking
mode

Reported-by: Andrew Baumann <Andrew.Baumann@microsoft.com>
Reported-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-Id: <1458324041-22709-1-git-send-email-berrange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>