Add method to update a disk object size
Add method to update a disk object size

This patch adds a method that implements updating of a disk
(object.Disk) size, together with its children.

While this will not track the exact disk size, it allows at least an
approximate size to be recorded in the configuration (and queried).

Reviewed-by: imsnah


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