Gentoo's hostname file format instead of being just the host name
is hostname=thename". The old code works fine when the file has no comments
but if there is a comment the line

```
gentoo_hostname_config = 'hostname="%s"' % conf
```

can render an invalid hostname file that looks similar to

```
hostname="#This is the host namehello"
```

The fix inserts the hostname in a gentoo friendly way so that it gets
handled by HostnameConf as a whole and comments are handled and preserved