add create_stemcell and delete_stemcell

Change-Id: I928ce78a7ff9c0175e8ffd05bf923dcf8040ab41
create_vm done without recompose vapp
add has_vm?
add reboot_vm and partially recompose_vapp
configure_networks and delete_vm
partial complete all CPIs
simplify wait task logic
complete disk-related features
unify errors
add timed loop for retries
fix RecomposeVAppParams add child namespace prefix
flush cache after vapp created/deleted
bugfix: 54418438: delete environment iso after vm is deleted
workaround for delete vApp containing a single VM
fix default vApp name and add retry logic for rest calls
fix tasks method of XML wrapper Media
merge Harsh's fix for delete deployment
Merge branch 'refactor-conn'