Race in NodeStorageService.store

[rymsha]

It may theoretically happen in

• node with the id does not exist
• node id is exactly the same
• two threads or instances write at the same time
• one thread/instance manages to overtake another

nodeServvice.checkExists <- return false for thread 1 and 2
versionIndex.store
branchIndex.store 
<-------------------- thread 2 overtakes thread 1
searchIndex.store

in this case branchIndex will have data for thread 2 (last write wins) but searchIndex will have data for thread 1

If nodes are different (data, path, permissions, etc) it is a big problem. For entirely equal nodes search index will have wrong nodeVersion Id (it is called _versionkey in search index) and maybe timestamp (_ts).