Fix multiple deferred indexes failure

Couchmove now ignores index building failure caused by a Build Already In Progress error. This can typically happens when you have multiple changelogs containing N1QL indexes deferred build. The index will still be built in the background.

see https://forums.couchbase.com/t/build-index-fails-index-xxx-yyy-zzz-idx-will-retry-building-in-the-background-for-reason-build-already-in-progress/16556