Add a new type ClusterData
Add a new type ClusterData

This will be used to hold all the disparate uses of the cluster data:
we have either tuples with these four elements, or functions taking
these four arguments, etc.

Signed-off-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>
Reviewed-by: Balazs Lecz <024c580adbe3324c61e798a30c60cf94ec02e89f@google.com>

ganeti/ganeti,ganeti/ganeti,ganeti-github-testing/ganeti-test-1,bitemyapp/ganeti,apyrgio/ganeti,grnet/snf-ganeti,ganeti-github-testing/ganeti-test-1,grnet/snf-ganeti,yiannist/ganeti,andir/ganeti,yiannist/ganeti,dimara/ganeti,mbakke/ganeti,bitemyapp/ganeti,andir/ganeti,dimara/ganeti,apyrgio/snf-ganeti,mbakke/ganeti,mbakke/ganeti,leshchevds/ganeti,apyrgio/snf-ganeti,ganeti/ganeti,apyrgio/ganeti,leshchevds/ganeti,andir/ganeti,onponomarev/ganeti,yiannist/ganeti,onponomarev/ganeti,leshchevds/ganeti