localnetworkhelper: make CommandName available to all platforms

Make localnetworkhelper package compileable on all platforms (#36)

Periodically perform cluster health checks (#35)

And publish them as "org.cirruslabs.chacha.cluster.health" metric.

Use different logging levels depending on the resulting status code (#34

)

* Use different logging levels depending on the resulting status code

And also document "direct-connect-header" option.

* Log upstream response using %+v instead of just %v

Make direct connect header optional (#32)

Do not use request.URL instead of directConnectURL

Use metric.WithExplicitBucketBoundaries() (#30)

Unlock localnetworkhelper and obey ctx in PrivilegedDialContext() (#25)

Revert "localnetworkhelper: support context.Context and avoid using s…

…ync.Mutex (#21)" (#24)

localnetworkhelper: ensure permissions on a socket allow incoming con…

…ns. (#22)

* localnetworkhelper: ensure permissions on a socket allow incoming conns.

* Better errors when chmod(2) fails