Don't reuse failed plans.

Failed plans get re-appended to the list of plans unconditionally.
 
https://github.com/apache/beam/blob/cf8ffe660cfcb1f7d421171f406fa991b93e043b/sdks/go/pkg/beam/core/runtime/harness/harness.go#L315
 
Which means there's a risk that a new bundle using the same bundle descriptor might re-use a failed plan. 
 
https://github.com/apache/beam/blob/cf8ffe660cfcb1f7d421171f406fa991b93e043b/sdks/go/pkg/beam/core/runtime/harness/harness.go#L236
 
While users should be resetting everything in StartBundle, that's not necessarily the case. It would be easier on users when plans are re-used to recreate them on failures.
 
After a certain point plans are garbage collected already, both failed and successful.