test-qga: Avoid qobject_from_jsonv("%"PRId64)

The qobject_from_jsonv() function implements a pseudo-printf
language for creating a QObject; however, it is hard-coded to
only parse a subset of formats understood by -Wformat, and is
not a straight synonym to bare printf().  In particular, any
use of an int64_t integer works only if the system's
definition of PRId64 matches what the parser expects; which
works on glibc (%lld or %ld depending on 32- vs. 64-bit) and
mingw (%I64d), but not on Mac OS (%qd).  Rather than enhance
the parser, it is just as easy to use normal printf() for
this particular conversion, matching what is done elsewhere
in this file [1], which is safe in this instance because the
format does not contain any of the problematic differences
(bare '%' or the '%s' format).

The use of PRId64 for a variable named 'pid' is gross, but it
is a sad reality of the 64-bit mingw environment, which
mistakenly defines pid_t as a 64-bit type even though getpid()
returns 'int' on that platform [2].  Our definition of the
QGA GuestExec type defines 'pid' as a 64-bit entity, and we
can't tighten it to 'int32' unless the mingw header is fixed.
Using 'long long' instead of 'int64_t' just so that we can
stick with qobject_from_jsonv("%lld") instead of printf() is
not any prettier, since we may have later type churn anyways.

[1] see 'git grep -A2 strdup_printf tests/test-qga.c'
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1397787

Reported by: G 3 <programmingkidx@gmail.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1479922617-4400-3-git-send-email-eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
