validate_resharding_after_refresh misusing follow_system_log

[fruch]

this functions is doing a call like that:

resharding_logs = list(system_log_follower)

and expects the log line to be available right after that line.

that is not how the iterator give from follow_system_log should be use,
it should be read again and again in a loop until we get what we expect or timeout

we should introduce a helper function, or a method on this iterator, to be able to achieve that, with a timeout
and look for more naive usages of follow_system_log and address them

Ref: #4341

[fruch]

looks like this issue is incorrect, and failure cause of this are related to other issue, and should be investigated