Refactor common/utils methods to common/ondisk

Place all the methods related to on-disk layout and / or configuration
into a new common module that can be shared by the various modules
using the same on-disk layout.

Change-Id: I27ffd4665d5115ffdde649c48a4d18e12017e6a9
Signed-off-by: Peter Portante <peter.portante@redhat.com>
Refactor on-disk knowledge out of object server

Refactor on-disk knowledge out of the object server by pushing the
async update pickle creation to the new DiskFileManager class (name is
not the best, so suggestions welcome), along with the REPLICATOR
method logic. We also move the mount checking and thread pool storage
to the new ondisk.Devices object, which then also becomes the new home
of the audit_location_generator method.

For the object server, a new setup() method is now called at the end
of the controller's construction, and the _diskfile() method has been
renamed to get_diskfile(), to allow implementation specific behavior.

Change-Id: Id945276037dbbeb8a778753e47a7316cd408eac7
Signed-off-by: Peter Portante <peter.portante@redhat.com>
Use new ondisk.Devices where possible

We also remove the unused mount_check attribute from the recon
middleware.

Change-Id: Icc593fd548a6e2d9bc5c8178f78424b1d6473f05
Signed-off-by: Peter Portante <peter.portante@redhat.com>