Replacing non-inclusive term blacklist with neutral language

[chetanugale]

Fixes #1611

[untergeek]

Stale. To have this PR considered, the following conditions must be met:

• Re-open (prefer re-create) against current branches (must also include 6.x and 7.x)
• Will not accept a PR that results in existing configurations failing. In other words, blacklist must remain acceptable and not break or prevent an existing user's script from functioning after an upgrade. I appreciate what you're doing here, but breaking existing functionality is not acceptable. We can log a deprecation message if blacklist is used, but its presence must not break functionality and usability. We can fully remove in a major version release, but not until it's been deprecated and logged as such for quite a while.
• Will not accept a PR that doesn't address documentation in both the rST/Sphinx ReadTheDocs documentation as well as the asciidoc docs that render on elastic.co). Change like this must be adequately documented. Cannot just drop this on users without explanation, warning, documentation and examples.