Add system_vdiskmanager stage for vsphere
Add load_vmdk_settings logic for vsphere in bosh_agent
Add srm feature in vsphere cpi to read settings from vmdk
Add unit test in vsphere cpi for methods attach_independent_disk, detach_independent_disk, set_vmdk_content, attach_disk, detach_disk and configure_networks
Add system_vmdk_template stage in stemcell builder
Update bosh_agent to use vmdk template workflow to load settings
Update vsphere cpi to use vmdk template workflow
Remove system_vdiskmanager stage in vsphere