Including vl->type, even when vl->type_instance is available to avoid ov...

Including vl->type, even when vl->type_instance is available to avoid over-writing values (i.e. with the 'df' plugin).

We're hitting [this code path](https://github.com/collectd/collectd/blob/master/src/write_tsdb.c#L391) for submitting stats to opentsdb.

The problem is that [`df_complex` values](https://github.com/collectd/collectd/blob/master/src/df.c#L300) are being overwritten by [`df_inodes` values](https://github.com/collectd/collectd/blob/master/src/df.c#L354) when we also capture inodes.

This is probably happening elsewhere, as well.