Skip tests that require a specific version of the protocol if that version
is disabled at compile time.
This commit only partially does the job, mostly covering tests that check
the protocol version in client or server logs. It is not intended to be
exhaustive; in particular many uses of force_version are not covered (I
think they should instead be covered automatically, but this is out of scope
of the current commit).
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>