test_driver: Replace magic constant

In testOpenDefault we create a virtual computer that is later
presented to user. We also pretend to have NUMA cells and
initialize them somehow. But whilst doing so a magical constant
is used. Drop it.
Signed-off-by: NTomáš Ryšavý <tom.rysavy.0@gmail.com>
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/test/test_driver.c

@@ -1264,7 +1264,7 @@ testOpenDefault(virConnectPtr conn)
 
     /* Numa setup */
     privconn->numCells = 2;
-    for (u = 0; u < 2; ++u) {
+    for (u = 0; u < privconn->numCells; ++u) {
         privconn->cells[u].numCpus = 8;
         privconn->cells[u].mem = (u + 1) * 2048 * 1024;
     }