Move compute_topic into nova.compute.rpcapi

Even though the compute_topic opt is used outside nova.compute.rpcapi,
it makes sense for the RPC module to "own" the topic option.

blueprint: scope-config-opts
Change-Id: I453951825481b9a5ba1865f6bf1223f7b1e25f98
Move manager options into nova.service

Move the compute_manager, console_manager, cert_manager, network_manager
and scheduler_manager options into nova.service.

Apart from the tests, these options are mostly just used in nova.service
so it makes sense for them to live there. Also, metadata_manager already
lives there.

blueprint: scope-config-opts
Change-Id: I180859817b57c081b83d6a6f075a6ff76bb0ef6d
Move api_class options to where they are used

The compute_api_class, network_api_class and volume_api_class options
are only used in their respective modules, so move them there.

blueprint: scope-config-opts
Change-Id: Ib0497f46b44c4b3af7319550cc64c09d629ea362
Move osapi_compute_unique_server_name_scope to db

This strange little option is only used within the DB layer.

blueprint: scope-config-opts
Change-Id: I10b0fef02a5fffd44094fe351cde683fc5c31442
Move default_instance_type into nova.compute

Apart from the tests, this option is only used in
nova.compute.instance_types so move it there.

blueprint: scope-config-opts
Change-Id: Iadf4011739e50455b7ad4214a778a02e244fef35
Move common virt driver options to virt.driver

The default_ephemeral_format and use_cow_images options are used by a
number of virt drivers and nowhere else.

blueprint: scope-config-opts
Change-Id: I4ab2891e156589ae7bb44e6ce69cba3680a070c5