When a retry controller is added to a nested flow, with the exception of
AlwaysRetryAll, existing retry controllers do not cause a revert of
predecessor tasks in the surrounding flow. This is due to the fact that
these retry controllers always return RETRY.
The revert_all option, when set True, will result in the retry
controller returning REVERT_ALL rather than REVERT, which will cause
predecessor tasks in the surrounding flow to also be REVERTed.
Change-Id: I2d867b2d05e8559121ec48fd7249f15078450532