V2: State values now reported in lowercase, HEALTHY is now healthy

[cmacknz]

This has broken several automated health checking tests internally. If this was not intentionally we should revert to the original uppercase names to avoid causing similar issues for users.

Example one: elastic/elastic-package#1042
Example two: #1731 (comment)

[cmacknz]

FYI @axw, @jsoriano, @mrodm we are restoring the agent states to upper case, the APM and Integrations health checks in tests will have to be adjusted again.

We didn't do this intentionally, and we don't want anything users might similarly have written to break unexpectedly.