Support custom service endpoint hostname in info provider script.

Adds an extra optional option -s <nodename>

```bash
voms-config-info-providers -s <site_name> [-e] [-s <service hostname>}
```

so a non canonical hostname can be passed into the infromation system. 

In addition removes the assumption that 
```bash
$(hostname) == $(hostname -f)
```
which is not always true.