Right now, the stream stuff assumes that a stream is always
going to be used for transmit.  This is not the case, and in
fact doesn't work with the tunnelled migration stuff.  Add
a flag to remoteClientStream() to allow it to do RX only.
Signed-off-by: NChris Lalancette <clalance@redhat.com>

* daemon/dispatch.c: Set streamTX flag on outgoing data packets
* daemon/qemud.h: Add streamTX flag to track outgoing data
* daemon/qemud.c: Re-enable further TX when outgoing data packet
  has been fully sent.
* daemon/stream.h, daemon/stream.c: Add method for enabling TX.
  Support reading from streams and transmitting data out to client

* daemon/stream.c: Handle incoming stream data packets, queuing until
  stream becomes writable. Handle stream completion handshake
* po/POTFILES.in: Add daemon/stream.c

Defines the extensions to the remote protocol for generic
data streams. Adds a bunch of helper code to the libvirtd
daemon for working with data streams.

* daemon/Makefile.am: Add stream.c/stream.h to build
* daemon/stream.c, qemud/stream.h: Generic helper functions for
  creating new streams, associating streams with clients, finding
  existing streams for a client and removing/deleting streams.
* src/remote/remote_protocol.x: Add a new 'REMOTE_STREAM' constant
  for the 'enum remote_message_type' for encoding stream data
  in wire messages. Add a new 'REMOTE_CONTINUE' constant to
  'enum remote_message_status' to indicate further data stream
  messsages are expected to follow.  Document how the
  remote_message_header is used to encode data streams
* src/remote/remote_protocol.h: Regenerate
* daemon/dispatch.c: Remove assumption that a error message
  sent to client is always type=REMOTE_REPLY. It may now
  also be type=REMOTE_STREAM. Add convenient method for
  sending outgoing stream data packets. Log and ignore
  non-filtered incoming stream packets. Add a method for
  serializing a stream error message
* daemon/dispatch.h:  Add API for serializing stream errors
  and sending stream data packets
* daemon/qemud.h: Add struct qemud_client_stream for tracking
  active data streams for clients. Tweak filter function
  operation so that it accepts a client object too.
* daemon/qemud.c: Refactor code for free'ing message objects
  which have been fully transmitted into separate method.
  Release all active streams when client shuts down. Change
  filter function to be responsible for queueing the message