Makes opening/creating BatchingNeoStores more robust

There were some cases w/ restart shown by RestartableImportIT
that these additions takes care of.

community/kernel/src/main/java/org/neo4j/unsafe/impl/batchimport/store/BatchingNeoStores.java

@@ -73,6 +73,7 @@
 import static org.neo4j.helpers.collection.MapUtil.stringMap;
 import static org.neo4j.io.IOUtils.closeAll;
 import static org.neo4j.io.pagecache.IOLimiter.unlimited;
+import static org.neo4j.kernel.impl.index.labelscan.NativeLabelScanStore.getLabelScanStoreFile;
 import static org.neo4j.kernel.impl.store.MetaDataStore.DEFAULT_NAME;
 import static org.neo4j.kernel.impl.store.StoreType.PROPERTY;
 import static org.neo4j.kernel.impl.store.StoreType.PROPERTY_ARRAY;
@@ -133,7 +134,7 @@ private BatchingNeoStores( FileSystemAbstraction fileSystem, PageCache pageCache
         this.externalPageCache = externalPageCache;
     }
 
-    private boolean databaseExistsAndContainsData( PageCache pageCache, File storeDir )
+    private boolean databaseExistsAndContainsData()
     {
         File metaDataFile = new File( storeDir, StoreType.META_DATA.getStoreFile().fileName( StoreFileType.STORE ) );
         try ( PagedFile pagedFile = pageCache.map( metaDataFile, pageCache.pageSize(), StandardOpenOption.READ ) )
@@ -161,10 +162,12 @@ private boolean databaseExistsAndContainsData( PageCache pageCache, File storeDi
      */
     public void createNew() throws IOException
     {
-        if ( databaseExistsAndContainsData( pageCache, storeDir ) )
-        {
-            throw new IllegalStateException( storeDir + " already contains data, cannot do import here" );
-        }
+        assertDatabaseIsEmptyOrNonExistent();
+
+        // There may have been a previous import which was killed before it even started, where the label scan store could
+        // be in a semi-initialized state. Better to be on the safe side and deleted it. We get her after determining that
+        // the db is either completely empty or non-existent anyway, so deleting this file is OK.
+        fileSystem.deleteFile( getLabelScanStoreFile( storeDir ) );
 
         instantiateStores();
         neoStores.getMetaDataStore().setLastCommittedAndClosedTransactionId(
@@ -173,6 +176,14 @@ public void createNew() throws IOException
                 initialIds.lastCommittedTransactionLogVersion() );
     }
 
+    public void assertDatabaseIsEmptyOrNonExistent()
+    {
+        if ( databaseExistsAndContainsData() )
+        {
+            throw new IllegalStateException( storeDir + " already contains data, cannot do import here" );
+        }
+    }
+
     /**
      * Called when expecting a previous attempt/state of a database to open, where some store files should be kept,
      * but others deleted. All temporary stores will be deleted in this call.
@@ -186,8 +197,6 @@ public void pruneAndOpenExistingStore( Predicate<StoreType> mainStoresToKeep, Pr
         deleteStoreFiles( TEMP_NEOSTORE_NAME, tempStoresToKeep );
         deleteStoreFiles( DEFAULT_NAME, mainStoresToKeep );
         instantiateStores();
-        neoStores.makeStoreOk();
-        temporaryNeoStores.makeStoreOk();
     }
 
     private void deleteStoreFiles( String storeName, Predicate<StoreType> storesToKeep )
@@ -227,6 +236,9 @@ private void instantiateStores() throws IOException
                 neoStores.getRelationshipTypeTokenStore() );
         temporaryNeoStores = instantiateTempStores();
         instantiateKernelExtensions();
+
+        neoStores.makeStoreOk();
+        temporaryNeoStores.makeStoreOk();
     }
 
     private NeoStores instantiateTempStores()