Move fake_network config option to linux_net

Option 'fake_network' is used by nova/network/linux_net.py but not
imported from nova/network/manager.py. Both use it, but manager imports
linux_net (via nova/network/api.py + nova/network/floating_ips.py) so it
makes more sense to define the option in linux_net and import_opt in
manager.

Precise example import chain:
    bin/nova-manage
    nova/cmd/manage.py: import_opt('flat_network_bridge', 'nova.network.manager')
    nova/network/manager.py: from nova.network import api as network_api
      -- At this point, manager has started to import but not yet called
      register_opts
    nova/network/api.py: from nova.network import floating_ips
    nova/nova/network/floating_ips.py: import_opt('public_interface', 'nova.network.linux_net')
    nova/nova/network/linux_net.py: import_opt('fake_network', 'nova.network.manager')
      -- BANG! Manager hasn't registered the option we want to import

Change-Id: I66f021b34aef650dca148a58203c249f6aa0e83e
XenAPI: get_info was very expensive

Getting the whole VM record is expensive and slowed down Tempest tests
significantly.  Replaced with getting each required item.

When getting power state, only need that specific value, so reduce the
calls to get_info too.

Change-Id: I93bcef5b692a531aac41518dc29d5d4f46cded65
Merge "XenAPI: get_info was very expensive"
Merge "Move fake_network config option to linux_net"