qemu-char: rewrite io_channel_send_all and drop the '_all' suffix

qemu-char: rewrite io_channel_send_all and drop the '_all' suffix

The current code is oddly written and have equally odd semantics.
Despite the '_all' suffix, upon EAGAIN the result will be a partial
write but instead of returning the partial write, we return EAGAIN.

Change the behavior to write as much as we can until we get an EAGAIN
returning a partial write if we do.

Reported-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Message-id: 1364575190-731-1-git-send-email-aliguori@us.ibm.com