Added FQDN append feature

Hi,

For my own needs (Influx/Grafana integration), I wanted to have host FQDN included in raw data structure.
To do that, I added a new boolean argument (optional) to directly append FQDN in injected raw data.

__default behaviour :__
```
> ./sysinfo_influxdb -c="mem,uptime,swap"

#0: server-01.mem
| free	| used	| actualfree	| actualused	| total	|
| 5484720128	| 2749816832	| 6962950144	| 1271586816	| 8234536960	| 

#1: server-01.uptime
| length	|
| 25474	| 

#2: server-01.swap
| free	| used	| total	|
| 4094685184	| 0	| 4094685184	|
```

__new behaviour with FQDN flag:__
```
> ./sysinfo_influxdb -c="mem,uptime,swap" -P="metrics" --fqdn

#0: metrics.swap
| free	| used	| total	| fqdn	|
| 4094685184	| 0	| 4094685184	| server-01.mycompany.com	| 

#1: metrics.mem
| free	| used	| actualfree	| actualused	| total	| fqdn	|
| 5507203072	| 2727333888	| 6971310080	| 1263226880	| 8234536960	| server-01.mycompany.com	| 

#2: metrics.uptime
| length	| fqdn	|
| 25652	| server-01.mycompany.com	|
```

Hope this will help people, I'm sure that this data structure can really be interesting when using some kind of queries.
Thanks for reviewing & testing this ! I'm totally a Go-newbie so don't hesitate to fix some of my loops / if or global logic :-) !

Barth