remove index option from scripts and reimplement it for backup

[haarg]

The index option is meant to control the index that has all of our ES data. But in the future, each document type will need to be in a separate index. So the idea of having a global configurable index doesn't make sense.

The backup script needs to be able to operate on all indexes, and works generically with any type. Reimplement an index option for it, allowing multiple indexes to be specified.

[mickeyn]

is this change assuming we only work with cpan index? we do have multiple indices (all new types have their own index) and backup should be able to handle them.

[haarg]

With this PR, the backup script only requires the --index option, instead of also requiring the ES_SCRIPT_INDEX environment variable. None of the other scripts have any use for the --index option or the ES_SCRIPT_INDEX env var, because they are either using cpan_v1_01 or their own index that is defined in the code.

[haarg]

I guess I didn't entirely answer your question. No, this isn't only assuming we only use the cpan index. It's just making it so the use of cpan_v1_01 is not configurable. This is so the rest of the code can be updated to refer directly to their index, rather than trying to use a dynamic value. I'm intending to set up some infrastructure to make it easy to switch the index/type of each of the current "types", so we can move to one type per index.