[Reviewer Andy] Run chef-client niced when clustering nodes

Andy

Can you review the fix for running chef-client niced when clustering.

I've also pulled in your change to ensure Cassandra isn't niced when it is restarted from chef-client, except that I've made it dependent on the current nice level rather than have it assume 19 (a bit fiddly to make it work with both positive and negative values of nice, but I've tested it with +ve, -ve and zero values and it does the right thing) - shout if you think there is a more elegant way.

Mike