tests: use g_strdup instead of VIR_STRDUP

Replace all occurrences of
  if (VIR_STRDUP(a, b) < 0)
     /* effectively dead code */
with:
  a = g_strdup(b);

Signed-off-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

tests/virtestmock.c

@@ -122,8 +122,7 @@ checkPath(const char *path,
     } else {
         /* Yeah, our worst nightmares just became true. Path does
          * not exist. Cut off the last component and retry. */
-        if (VIR_STRDUP_QUIET(crippledPath, relPath ? relPath : path) < 0)
-            goto error;
+        crippledPath = g_strdup(relPath ? relPath : path);
 
         virFileRemoveLastComponent(crippledPath);