MINOR: haproxy: Add an command option to disable data fast-forward

The -dF option can now be used to disable data fast-forward. It does the
same than the global option "tune.fast-forward off". Some reg-tests may rely
on this optim. To detect the feature and skip such script, the following
vtest command must be used:

  feature cmd "$HAPROXY_PROGRAM -cc '!(globa.tune & GTUNE_NO_FAST_FWD)'"
3 files changed