Retry any Datastore reads in EppResource map-reduce input

Datastore has a non-zero chance of failing on reads. A map-reduce with too many
failures will eventually give up. As a result, any map-reduce that goes over a
large number of datastore entities is almost guaranteed to fail.

Since we expect to have a large number of EppResources, we make sure to wrap
all datastore reads with some retrying mechanism to reduce the number of
transient failures that propagate to Map-Reduce.

This feature already existed for CommitLogManifestReader, we refactor the code to use the same retrying mechanism in EppResource readers.

Also removed the transactNew around the reads because looking at the source - it doesn't actually do anything we need (doesn't retry on any failure other than concurrency failure)

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=190633281

java/google/registry/mapreduce/inputs/EppResourceEntityReader.java

@@ -56,9 +56,9 @@ class EppResourceEntityReader<R extends EppResource> extends EppResourceBaseRead
    */
   @Override
   public R next() throws NoSuchElementException {
-    // Loop until we find a value, or nextEri() throws a NoSuchElementException.
+    // Loop until we find a value, or nextQueryResult() throws a NoSuchElementException.
     while (true) {
-      Key<? extends EppResource> key = nextEri().getKey();
+      Key<? extends EppResource> key = nextQueryResult().getKey();
       EppResource resource = ofy().load().key(key).now();
       if (resource == null) {
         logger.severefmt("EppResourceIndex key %s points at a missing resource", key);