Robot: Fix error handling in retry procedure.
Robot: Fix error handling in retry procedure.

The NeedsRetry call was returning pointers to TaskRetryErrors, which
does not fulfil the type assertion checked for in RetryFunction.
Bug manifested as retries causing immediate failure, and no output
generated for failing calls.

dsrbecky/gapid,baldwinn860/gapid,google/gapid,google/gapid,Qining/gapid,pmuetschard/gapid,google/gapid,Qining/gapid,baldwinn860/gapid,google/gapid,google/agi,Qining/gapid,google/agi,dsrbecky/gapid,Qining/gapid,Qining/gapid,pmuetschard/gapid,dsrbecky/gapid,google/agi,pmuetschard/gapid,dsrbecky/gapid,google/agi,google/agi,baldwinn860/gapid,pmuetschard/gapid,pmuetschard/gapid,baldwinn860/gapid,ek9852/gapid,google/gapid,pmuetschard/gapid,ek9852/gapid,Qining/gapid,pmuetschard/gapid,ek9852/gapid,google/agi,dsrbecky/gapid,dsrbecky/gapid,Qining/gapid,ek9852/gapid,baldwinn860/gapid,ek9852/gapid,google/gapid,dsrbecky/gapid,ek9852/gapid,ek9852/gapid,google/gapid,baldwinn860/gapid,dsrbecky/gapid,baldwinn860/gapid,pmuetschard/gapid,google/gapid,Qining/gapid,google/agi,ek9852/gapid,google/agi,baldwinn860/gapid