fail: check condition only when its failpoint is open

[gengliqi]

Signed-off-by: Liqi Geng [email protected]

The check-condition code in failpoint runs all the time even it is not open. It may lead to bad performance if checking the condition is very expensive or misuse if someone modifies some variables in check-condition code and it's valid only when its failpoint is open. (my guess scenario)

[brson]

Here's a patch to fix CI: https://github.com/tikv/fail-rs/pull/49