replace use of gnulib snprintf by g_snprintf

Glib implementation follows the ISO C99 standard so it's safe to replace
the gnulib implementation.

Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>

tests/libxlmock.c

@@ -99,7 +99,7 @@ VIR_MOCK_IMPL_RET_ARGS(virFileMakePath, int,
 {
     /* replace log path with a writable directory */
     if (strstr(path, "/log/")) {
-        snprintf((char*)path, strlen(path), ".");
+        g_snprintf((char*)path, strlen(path), ".");
         return 0;
     }
     return real_virFileMakePath(path);