Performance Counter IntelliCache Cache hits + misses not handled

[cocoon]

I don't know if it can happen in a real environment, but I think if IntelliCache is available and one selects a server and it's performance tab it throws exceptions here:

https://github.com/xenserver/xenadmin/blob/master/XenAdmin/Controls/CustomDataGraph/DataSet.cs#L87

Because the following two cases are not handled:

case "hits/s":
case "misses/s":

It just happened when I tested it against a VM and thought I would let you know.

[kc284]

It could be a regression related to the logic changes in #2848, Thanks for reporting it, I'll have a look at it and fix accordingly.