Move instance_get_*() to conductor

This patch adds conductor support for instance_get_all_by_filters(),
and supports the following APIs through that method:

 - instance_get_all()
 - instance_get_all_by_host()
 - instance_get_all_by_filters()

Further, it adds support for the following APIs:

 - instance_get_all_hung_in_rebooting()
 - instance_get_active_by_window()

It also makes compute/manager use conductor for these operations, with
one exception. Currently, ComputeManager.init_host () lists all
instances associated with the host, which may happen before a conductor
service is available. This will be handled separately due to the
sequencing concerns.

Related to bp/no-db-compute-manager

Change-Id: I0dd346fd632aa15cd301386bc392502b95709529
Merge "Move instance_get_*() to conductor"