Monitor: Debug stray prints the right way

Monitor: Debug stray prints the right way

QObject Monitor handlers should not call any Monitor print
function: they should only build objects, printing is done
by common code.

Current QMP code will ignore such calls, as we can't send
garbage to clients, additionally it will also emit an
undefined error on the assumption that print calls usually
report errors.

However, the right way to deal with this is to rely on a
return code. This has been fixed by other commit already.

Now, this commit drops the error from monitor_vprintf() and
adds a better debugging mechanism for those 'stray' prints:
we count them if debug is enabled and let the developer know
if a QObject handler is trying to print anything.

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