Make detach_volume() use objects

This changes the detach_volume() method in compute manager to take
objects.

Related to blueprint compute-manager-objects-juno

Change-Id: Ia09415c55dee0d49e8925d6eb23737b55255d7e1
Finish _delete_instance() object conversion

The _delete_instance() helper has been using objects for a while
now, but was still using an old conductor method to actually
destroy the instance. This makes it use instance.destroy(). Since the
same thing happens under the covers, none of the tests need to be
changed.

Related to blueprint compute-manager-objects-juno

Change-Id: I413394bbc931d1011c276454ecb34ddd8d948f07
Updated from global requirements

Change-Id: I2378e9d68c9a8bd05fa8a086ce8e1c15bd0eb136
Merge "Updated from global requirements"