fixes #3698 - add image_id alias to server resource as form uses it

(cherry picked from commit 4f8049c586c066e1fac16825af06249cd46b7242)
fixes #2680 - ensure RbVmomi::VIM::ComputeResource is loaded before our ComputeResource

(cherry picked from commit 58547fc6413965e8491d72eb308e95caa3952dff)