lib: improve wait.For returns.

[ldez]

Fixes #1401

[quenbyako]

@ldez i though about something different which is using context with timeout)

something like

func For(ctx context.Context, repeatInterval time.Duration, f func() (bool, error)) error {
    ...
}

also, i don't think that it's a good idea to return last error: if f returns error, it must be throwed explicitly, cause you can lost more important errors in the middle of updating process.

[ldez]

For now, I don't want to change the signature of the function.

also, i don't think that it's a good idea to return last error: if f returns error, it must be throwed explicitly, cause you can lost more important errors in the middle of updating process.

this is the goal of this function to not throw an error immediately and to only return the last error.

[quenbyako]

@ldez return the last error

Ehhh, okay, it just looks pretty weird for me, but okay, you're a member and i'll not argue for my subjective opinion, so alright)

Also, thanks a lot for so fast fix and update! I really appreciate that 🤗

[dmke]

it just looks pretty weird for me

Naming is hard. A better name for For() would have been RetryUntil().