REGTEST/MINOR: Missing mandatory "ignore_unknown_macro".

REGTEST/MINOR: Missing mandatory "ignore_unknown_macro".

Since bbc34e2 varnish commit (for varnishtest), a new "cli"
macro is automatically created for each VTC script to dialog with
the CLI. Consequently, as this macro is unknown from higher level
code for varnishtest, it makes the scripts fail if we
we do not ask varnishtest to disregard the unknown macros.
To prevent this, from now on, for each VTC file for haproxy we MUST add
"feature ignore_unknown_macro" line to do so. This is mandatory