Add two new variables in the cluster score
Add two new variables in the cluster score

This patch adds two new variables to the cluster score:
  - variance of the failN1 attribute
  - variance of the reserved memory percentage

The variance of the failN1 helps make the cluster N+1 happy, whereas the
reserved memory percentage helps balance the unused memory for
redundancy on the nodes.
ganeti/ganeti,leshchevds/ganeti,apyrgio/snf-ganeti,yiannist/ganeti,mbakke/ganeti,andir/ganeti,onponomarev/ganeti,mbakke/ganeti,apyrgio/ganeti,dimara/ganeti,onponomarev/ganeti,andir/ganeti,leshchevds/ganeti,bitemyapp/ganeti,leshchevds/ganeti,dimara/ganeti,bitemyapp/ganeti,ganeti/ganeti,andir/ganeti,grnet/snf-ganeti,grnet/snf-ganeti,mbakke/ganeti,yiannist/ganeti,apyrgio/ganeti,apyrgio/snf-ganeti,ganeti-github-testing/ganeti-test-1,ganeti-github-testing/ganeti-test-1,ganeti/ganeti,yiannist/ganeti