kvm plugins improvements

I added a few improvements to the kvm plugins:

* Make most of them also work on RedHat based systems
* Add an additional kvm_net_rh Plugin that works on RedHat bases systems. It is more or less a copy of the existing kvm_net plugin, which does not work and which needed to many changes which I'm not sure would have broken things further.
This line seems to contain a bug, which should be fixed before we can merge.

    % cat /proc/net/dev | awk '{ print $1 ":" $9 }'    
    Inter-|:
    face:multicast|bytes
    eth0::0
    eth1::5246
    virbr0::0
    lo::0

The format on my box is:

    % cat /proc/net/dev
    Inter-|   Receive                                                |  Transmit
     face |bytes    packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carrier compressed
      eth0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0
      eth1: 3833806033 3143411    0    0    0     0          0      5246 168429641 1939069    0    0    0     0       0          0
    virbr0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0
        lo: 86071620  477326    0    0    0     0          0         0 86071620  477326    0    0    0     0       0          0

...which looks more human-readable than strictly parsable.

On a reasonably modern linux kernel, perhaps what you can find with "find /sys/class/net/*/statistics/" may be more useful.