QMP: Introduce qmp-shell

QMP: Introduce qmp-shell

This is a very simple shell written in Python for demonstration
purposes.

Unfortunately it's a bit awkward right now, as the user has
to specify the arguments names and the printed data can be
a raw dictionary or list, like the following example:

(QEMU) pci_add pci_addr=auto type=nic
{u'slot': 5, u'bus': 0, u'domain': 0, u'function': 0}
(QEMU)

It's worth to note that the shell is broken into two files.
One is the shell itself, the other is the QMP class which
handles the communication with QEMU.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>