Interface for entrylogger

Define the interface and contract for entrylogger. This is mostly
taking the entrylogger methods used by other components and prettying
them up a bit.

Notable changes are:
- internalReadEntry is now readEntry. There is no 'validate'
  flag. Instead there are two overloads for the method, and validation
  only runs if ledgerId and entryId are passed in.
- shutdown has been renamed to close.
- the compaction entrylog methods have been put behind an
  interface. As it was they were leaking implementation
  details. Ultimitely compaction itself should be hidden behind the
  entrylogger, but that's a larger refactor.

bookkeeper-server/src/main/java/org/apache/bookkeeper/bookie/AbstractLogCompactor.java

@@ -57,7 +57,10 @@ public AbstractLogCompactor(ServerConfiguration conf, LogRemovalListener logRemo
      */
     public void cleanUpAndRecover() {}
 
-    static class Throttler {
+    /**
+     * class Throttler.
+     */
+    public static class Throttler {
         private final RateLimiter rateLimiter;
         private final boolean isThrottleByBytes;
 

bookkeeper-server/src/main/java/org/apache/bookkeeper/bookie/CompactableLedgerStorage.java

@@ -22,7 +22,7 @@
 package org.apache.bookkeeper.bookie;
 
 import java.io.IOException;
-
+import org.apache.bookkeeper.bookie.storage.EntryLoggerIface;
 /**
  * Interface that identifies LedgerStorage implementations using EntryLogger and running periodic entries compaction.
  */
@@ -31,7 +31,7 @@ public interface CompactableLedgerStorage extends LedgerStorage {
     /**
      * @return the EntryLogger used by the ledger storage
      */
-    EntryLogger getEntryLogger();
+    EntryLoggerIface getEntryLogger();
 
     /**
      * Get an iterator over a range of ledger ids stored in the bookie.

bookkeeper-server/src/main/java/org/apache/bookkeeper/bookie/EntryLogCompactor.java

@@ -27,7 +27,10 @@
 import java.util.ArrayList;
 import java.util.List;
 
+import org.apache.bookkeeper.bookie.storage.EntryLogScanner;
+import org.apache.bookkeeper.bookie.storage.EntryLoggerIface;
 import org.apache.bookkeeper.conf.ServerConfiguration;
+
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -40,13 +43,13 @@ public class EntryLogCompactor extends AbstractLogCompactor {
     private static final Logger LOG = LoggerFactory.getLogger(EntryLogCompactor.class);
 
     final CompactionScannerFactory scannerFactory = new CompactionScannerFactory();
-    final EntryLogger entryLogger;
+    final EntryLoggerIface entryLogger;
     final CompactableLedgerStorage ledgerStorage;
     private final int maxOutstandingRequests;
 
     public EntryLogCompactor(
             ServerConfiguration conf,
-            EntryLogger entryLogger,
+            EntryLoggerIface entryLogger,
             CompactableLedgerStorage ledgerStorage,
             LogRemovalListener logRemover) {
         super(conf, logRemover);
@@ -82,9 +85,9 @@ public boolean compact(EntryLogMetadata entryLogMeta) {
     class CompactionScannerFactory {
         List<EntryLocation> offsets = new ArrayList<EntryLocation>();
 
-        EntryLogger.EntryLogScanner newScanner(final EntryLogMetadata meta) {
+        EntryLogScanner newScanner(final EntryLogMetadata meta) {
 
-            return new EntryLogger.EntryLogScanner() {
+            return new EntryLogScanner() {
                 @Override
                 public boolean accept(long ledgerId) {
                     return meta.containsLedger(ledgerId);