Add qemu-ga-client script

Add qemu-ga-client script

This is an easy-to-use QEMU guest agent client written in
Python. It simply provides commands to call guest agent
functions like ping, fsfreeze and shutdown. Additionally,
it provides extra useful commands, e.g, cat, ifconfig and
reboot, by using guet agent functions.

Examples:
  $ export QGA_CLIENT_ADDRESS=/tmp/qga.sock
  $ qemu-ga-client ping

  $ qemu-ga-client cat /etc/resolv.conf
  # Generated by NetworkManager
  nameserver 10.0.2.3

  $ qemu-ga-client fsfreeze status
  thawed
  $ qemu-ga-client fsfreeze freeze
  2 filesystems frozen

The script communicates with a guest agent by means of
qmp.QEMUMonitorProtocol. Every commands are called with
timeout (3 sec.) to avoid blocking. The script always
calls sync command prior to issuing an actual command
(except for ping which doesn't need sync).

Signed-off-by: Ryota Ozaki <ozaki.ryota@gmail.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>