Pass instance object to soft_delete() and get_info()

This makes compute manager pass an instance object to the
virt driver's soft_delete() and get_info method instead of a
dict primitive.

Related to blueprint virt-objects

Change-Id: I52aae532c08596d7a78a3e75f8b0869951fc8991
Merge "Pass instance object to soft_delete() and get_info()"