Found that in one previous commit

  42c64d06 ('test: fix hanging of vinyl/gh.test.lua')

Was mistakenly made such change:

  -while finished ~= 2 do fiber.sleep(0.01) end
  +test_run:wait_cond(function() return finished ~= 2 end)

And the logic of the check was broken. This patch fixes it.

Part of #5141
Fixes tarantool/test-run#261
Part of tarantool/tarantool-qa#106