vhost-user-test: Fix 'make check' broken on glib < 2.26

After commit 89b516d8, some logics is turbid and
breaks 'make check' as below errors:
tests/vhost-user-test.c: In function '_cond_wait_until':
tests/vhost-user-test.c:154: error: 'G_TIME_SPAN_SECOND' undeclared (first use in this function)
tests/vhost-user-test.c:154: error: (Each undeclared identifier is reported only once
tests/vhost-user-test.c:154: error: for each function it appears in.)
tests/vhost-user-test.c: In function 'read_guest_mem':
tests/vhost-user-test.c:192: warning: implicit declaration of function 'g_get_monotonic_time'
tests/vhost-user-test.c:192: warning: nested extern declaration of 'g_get_monotonic_time'
tests/vhost-user-test.c:192: error: 'G_TIME_SPAN_SECOND' undeclared (first use in this function)
make: *** [tests/vhost-user-test.o] Error 1

First, vhost-usr-test.c rely on glib-compat.h because
of using G_TIME_SPAN_SECOND [glib < 2.26] and g_get_monotonic_time(),
but vhost-usr-test.c defined QEMU_GLIB_COMPAT_H, which make
glib-compat.h will not be included.
Second, if we remove QEMU_GLIB_COMPAT_H definability in
vhost-usr-test.c, then we will get below warnings:

tests/vhost-user-test.c: In function 'read_guest_mem':
tests/vhost-user-test.c:190: warning: passing argument 1 of 'g_mutex_lock' from incompatible pointer type
tests/vhost-user-test.c:234: warning: passing argument 1 of 'g_mutex_unlock' from incompatible pointer type

That's because glib-compat.h redefine the g_mutex_lock/unlock
function. Those functions' arguments is CompatGMutex/CompatGCond,
but vhost-user-test.c is using GMutex/GCond, which cause the type
is not consistent.

We can rerealize those functions of vhost-user-test.c,
which need a lots of patches. Let's simply address it, and
leave this file alone.

Signed-off-by: Gonglei <arei.gonglei@huawei.com>
Message-id: 1415149259-6188-1-git-send-email-arei.gonglei@huawei.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>