[CORE] Don't handle FNF exceptions when reading snapshot

We used to handle FNF exceptions in the store when reading a snapshot.
For instance if we can't open a segments file for a given commit point
we just return an empty metadata object and tracelog the even. This can
cause shards to be false marked as corrupted if a shard is forcefully
removed while a recovery started at the same time. We should in general
bubble up these exceptions and let the caller decided how to handle the
IOExceptions.

Author: s1monw

src/main/java/org/elasticsearch/index/store/Store.java

@@ -381,7 +381,7 @@ private static final void failIfCorrupted(Directory directory, ShardId shardId)
     }
 
     /**
-     * This exists so {@link BloomFilteringPostingsFormat} can load its boolean setting; can we find a more straightforward way?
+     * This exists so {@link org.elasticsearch.index.codec.postingsformat.BloomFilterPostingsFormat} can load its boolean setting; can we find a more straightforward way?
      */
     public class StoreDirectory extends FilterDirectory {
 
@@ -468,14 +468,7 @@ ImmutableMap<String, StoreFileMetaData> buildMetadata(IndexCommit commit, Direct
             ImmutableMap.Builder<String, StoreFileMetaData> builder = ImmutableMap.builder();
             Map<String, String> checksumMap = readLegacyChecksums(directory);
             try {
-                final SegmentInfos segmentCommitInfos;
-                try {
-                    segmentCommitInfos = Store.readSegmentsInfo(commit, directory);
-                } catch (FileNotFoundException | NoSuchFileException ex) {
-                    // no segments file -- can't read metadata
-                    logger.trace("Can't read segment infos", ex);
-                    return ImmutableMap.of();
-                }
+                final SegmentInfos segmentCommitInfos = Store.readSegmentsInfo(commit, directory);
                 Version maxVersion = Version.LUCENE_3_0; // we don't know which version was used to write so we take the max version.
                 for (SegmentCommitInfo info : segmentCommitInfos) {
                     final Version version = info.info.getVersion();