Use authentication when looking up ES version if required.
Give a default value to auth parameter in _get_es_version.
Merge pull request #878 from DataDog/es-version-lookup-auth

Use authentication when looking up ES version if required.
Bump source install to 4.2.0
Update CHANGELOG.md
Update CHANGELOG.md
fix process check documentation
fix process check compatibility with psutils >= 2.0 (fixes #863)
Merge branch 'master' into omnibus_bundling