Undeprecate and rewrite `repeat_until_true` (#1209)
Undeprecate and rewrite `repeat_until_true` (#1209)

`repeat_until_true` is a useful function, on occasions where you want to
retry certain result values, whilst failing immediately on any exceptions.

Let's
 * extend `retry_until_success` with a few extra parameters
 * rewrite `repeat_until_true` to use it, hence gaining an iteration limit
 * Undeprecate it.

matrix-org/sytest,matrix-org/sytest