added APP_NOT_STAGED constant

Signed-off-by: Mike Gehard <mgehard@pivotallabs.com>
start and push are idempotent

Signed-off-by: Mike Gehard <mgehard@pivotallabs.com>
ui.Failed takes formatted args

Signed-off-by: Mike Gehard <mgehard@pivotallabs.com>
delete_service is idempotent

Signed-off-by: Mike Gehard <mgehard@pivotallabs.com>