Add system_open_vdiskmanager stage for vsphere
Add load_vmdk_settings logic for vsphere in bosh_agent
Add srm feature in vshpere cpi to read settings from vmdk
Add unit test for methods attach_independent_disk, detach_independent_disk and set_vmdk_content in cloud.rb of bosh_vsphere_cpi
Add unit test for create_vm in vsphere cpi