Push setup() code down into TPG from Target

Add a setup() classmethod to TPG, and push down all the code that is
for TPG (and sub-objects) into it. This helps Target.setup() be much
more understandable.

Signed-off-by: Andy Grover <agrover@redhat.com>
Change StorageObject.all() to not take a path parameter

We have cls.configfs_dir that we can use.

Signed-off-by: Andy Grover <agrover@redhat.com>
Further break up setup()

Move initializations into class setup() methods, from monolithic TPG
setup() method.

Change Target.setup() to not take 'storage_objects', since LUN setup is
using tcm.StorageObject.all() directly now.

Signed-off-by: Andy Grover <agrover@redhat.com>