Cleaning up failed indexes when using --use-alias

[llexical]

When using the --use-alias flag when reindexing: search_index --rebuild --use-alias if the index fails due to an errored document or any other potential issue the new index that was created is then left behind and not cleaned up. This means if you are trying to debug what is going on or have a bug that's causing issues you can end up with a lot of orphaned indexes hanging around which you need to manually go into remove.

A simple solution to this is to remove the new index you just created on failure. If people find those failed indexes useful then a flag could be used to tidy up the failed index to give people the choice.

I have solved a similar problem before and am more than happy to work on it if others think it's a good idea. More than happy for feedback etc. If there's another way around this problem I just haven't spotted I would appreciate being directed to the right place!