Bugfix: unmark TKO and stop sending probes only if we also recorded success
Bugfix: unmark TKO and stop sending probes only if we also recorded success

Summary:
The following scenario is possible:
1) send request A normally
2) send request B normally
3) request A times out, causing us to enter TKO state and start sending probes
4) request B returns normal reply; in the current logic we will _not_ recordSuccess,
but we _will_ stop sending probes, which gets us into an unrecoverable state.

Test Plan:
unit tests

Reviewed By: pavlo@fb.com

Subscribers: alikhtarov

FB internal diff: D1639793

Tasks: 5444294

Blame Revision: D1587681

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