s192 - retry if message says so

[jlorper]

Fixes

my best guess:
console link

2 ideas based on these logs:

1. the exception is wrapped in RuntimeException, so not handled

Caused by: java.lang.RuntimeException: com.google.cloud.datastore.DatastoreException: Optimstic transaction was aborted due to a conflict with another concurrent operation. 
This can occur when there are overlapping reads or writes by other transactions, 
causing contention with the current transaction. Please retry the transaction.

2. this DatastoreException is not retryable despite what the message says

This can occur when there are overlapping reads or writes by other transactions, 
causing contention with the current transaction. Please retry the transaction., code=ABORTED

Change implications

• breaking change to API? no
• changes dependencies? no