monitor: Convert do_info_cpus() to QObject

monitor: Convert do_info_cpus() to QObject

Each CPU information is stored in a QDict and the returned
QObject is a QList of all CPUs.

The QDict contains the following information:

- "CPU": cpu index
- "current": "yes" or "no"
- "pc": current PC
- "halted": "yes" or "no"

The user output in the Monitor should not change and the
future monitor protocol is expected to emit something like:

[ { "CPU": 0, "current": "yes", "pc": 0x..., "halted": "no" },
{ "CPU": 1, "current": "no",  "pc": 0x..., "halted": "yes" } ]

which corresponds to the following user output:

* CPU #0: pc=0x00000000fffffff0
CPU #1: pc=0x00000000fffffff0 (halted)

Patchworks-ID: 35352
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>