Fix format specifier for OOM test fprintfs

The testutils.c file had some fprintfs which had not been
converted from %d to %zu, when 'testCounter' change to be
a size_t. This was a build breaker if --enable-test-oom
was enabled
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

tests/testutils.c

@@ -717,9 +717,9 @@ int virtTestMain(int argc,
         approxAlloc = virAllocTestCount();
         testCounter++;
         if (virTestGetDebug())
-            fprintf(stderr, "%d) OOM...\n", testCounter);
+            fprintf(stderr, "%zu) OOM...\n", testCounter);
         else
-            fprintf(stderr, "%d) OOM of %d allocs ", testCounter, approxAlloc);
+            fprintf(stderr, "%zu) OOM of %d allocs ", testCounter, approxAlloc);
 
         if (mp) {
             size_t i;