Bugfix: Check if site is indexable before building index name

[oscarssanchez]

Description of the Change

It seems if you run the following command: wp elasticpress get-indexes on multisite, you will get a list of index names from all sites, even if you have specified a site to not be indexed.

The site won't actually be indexed, but the command will return how that name would look, regardless.

Alternate Designs

Benefits

Possible Drawbacks

Verification Process

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• [] My change requires a change to the documentation.
• [] I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

Changelog Entry