[feature request] Add database uptime to /debug/vars endpoint

[rossmcdonald]

Feature Request

Proposal:

Currently the database uptime is included in the output to SHOW DIAGNOSTICS, but is not included in the /debug/vars endpoint output.

Current behavior:

Uptime is not included in the /debug/vars output.

Desired behavior:

Uptime will be included in the /debug/vars output. Here are the vars from SHOW DIAGNOSTICS:

name: system
PID  currentTime                    started                        uptime
---  -----------                    -------                        ------
8850 2017-01-20T00:30:30.417981478Z 2017-01-20T00:30:21.130836519Z 9.287145055s

Use case:

If uptime was exposed, Kapacitor could be used to monitor when the InfluxDB process crashes or restarts.