CLOUDSTACK-7871: allow VM and template details update using update APIs

Allows updating details (key/value) pair which updates entries in
vm_template_details and user_vm_details tables using updateVM and updateTemplate
APIs. This allows sys admins to update nics, controllers etc without DB hacking.

Signed-off-by: Rohit Yadav <rohit.yadav@shapeblue.com>