CLOUDSTACK-595 : Recreate root volume scenarios doesn't work in vmware

Issue seen during system vm template upgrade and restoreVM command
scenarios for vmware. In these cases CS tries to recreate root disk with
same name as the existing one, in case of vmware this results in creation
of vmdk file with same name for both existing and new root volume.
This results in undesired behavior when storage cleanup thread tries to
cleanup old volume. Made the vmdk file name unique by adding the volume
id to it. This will ensure that during volume recreation in the scenarios
mentioned vmdk will get created with a new name and there will be
no undesired side effects of running the storage cleanup thread.