gentoo: fix hostname rendering when value has a comment (#611)

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

1 files changed, 6 insertions, 4 deletions

diff --git a/cloudinit/distros/gentoo.py b/cloudinit/distros/gentoo.py
index 2bee1c89..e9b82602 100644
--- a/cloudinit/distros/gentoo.py
+++ b/cloudinit/distros/gentoo.py
@@ -160,10 +160,12 @@ class Distro(distros.Distro):
             pass
         if not conf:
             conf = HostnameConf('')
-        conf.set_hostname(your_hostname)
-        gentoo_hostname_config = 'hostname="%s"' % conf
-        gentoo_hostname_config = gentoo_hostname_config.replace('\n', '')
-        util.write_file(out_fn, gentoo_hostname_config, 0o644)
+
+        # Many distro's format is the hostname by itself, and that is the
+        # way HostnameConf works but gentoo expects it to be in
+        #     hostname="the-actual-hostname"
+        conf.set_hostname('hostname="%s"' % your_hostname)
+        util.write_file(out_fn, str(conf), 0o644)
 
     def _read_system_hostname(self):
         sys_hostname = self._read_hostname(self.hostname_conf_fn)