Add option to check-http for printing part of res.body

A new option to display a chosen number of bytes of data returned in the HTTP response body. Default behaviour is OFF.

Use Case: you have a /healthcheck endpoint that returns certain information which is useful to know via the Sensu dashboard/api rather than digging into further tools/logs to see why a 4XX or 5XX occurred. Saves valuable time when investigating alerts.

Added to all responses for consistency.