support set timezone in ConfigDB

[richard28530]

- What I did
support set timezone in ConfigDB

- How I did it
add a service at startup to proceed this

add timezone in DEVICE_METADATA::localhost

    "DEVICE_METADATA": {
        "localhost": {
            "hwsku": "INGRASYS-S9130-32X",
            "default_bgp_status": "up",
            "hostname": "S9130-LC-02",
            "timezone": "Asia/Shanghai",
            "platform": "x86_64-ingrasys_s9130_32x-r0",
            "mac": "6c:ec:5a:08:44:09",
            "default_pfcwd_status": "disable",
            "bgp_asn": "1400",
            "fast_reboot": "False",
            "deployment_id": "None",
            "type": "LeafRouter"
        }
    },

Here is the timezone value list
https://en.wikipedia.org/wiki/List_of_tz_database_time_zones

- How to verify it
set the corresponding time, check the date command output.

- Description for the changelog

[jleveque]

Suggest if [ -n "$TIMEZONE" ] to test for non-zero length.

[richard28530]

modified as you suggested

[jleveque]

Please also add double-quotes around $TIMEZONE as I suggested.

[richard28530]

Please also add double-quotes around $TIMEZONE as I suggested.
done

[lguohan]

this is a typical linux configuration, as you know, the config db cannot be a place to control every linux configuration. therefore, there needs to be some boundary that some configuration belongs to config db, some configuration do not belong to config db. This is a hard question. We need to stop at somewhere.

[richard28530]

this is a typical linux configuration, as you know, the config db cannot be a place to control every linux configuration. therefore, there needs to be some boundary that some configuration belongs to config db, some configuration do not belong to config db. This is a hard question. We need to stop at somewhere.

I think timezone has no difference with ntp/hostname.
If this is done in configdb, then you should do every time you update OS or backwards OS.

[rameshsanth]

Thanks for taking care of this. It is a useful feature

[rameshsanth]

Aren't these already run as root ? Why need "sudo bash -c " ?
Could you use "timedatectl settimezone US/Pacific" to set the timezone instead of directly modifying the files ?

[richard28530]

I left previous company i can't modify this pull request any more.