cyclades: Fix issue with storing images

The 'get_or_create' method should be used only for the 'uuid' and
'version' parameters.  Otherwise, any change of the image (e.g.
location) would cause the creation of a new image which would result in
integrity error.
cyclades: Pass the size of volume's origin

..to Archipelago, as 'origin_size' parameter.

Currently, the volume object is annotated with the size of the origin,
but this information is not stored in DB. This will have to be changed
when Synnefo supports detachable volumes.
cyclades: Fix wrong import
pithos: Improve test

Extend test for listing objects until a specific timestamp
to cover the case that an object is deleted after the provided timestamp.
pithos: PEP8 fix
pithos: Reset negative object sizes

Provide a database migration script that discovers
erroneously declared negative objects sizes and sets
them to 0.
pithos: Raise custom exception for invalid policies.

Raise 'InvalidPolicy' instead of 'ValuerError' exception
during account/container updates.
pithos: Change PithosBackendPool signature

PithosBackendPool constructor used to accept a number of keyword arguments
that it would pass them to the ModularBackend during the backend
instantiation.
Hence, this code required refactoring each time a new backend argument
was introduced.
This commit changes the PithosBackendPool to accept
a kwargs dictionary instead.
pithos: Recover 'get_domain_objects' from error case

Method 'get_domain_objects' should not fail if an object
(snapshot) is not available.
pithos: Fix sqlite backend
pithos: Refactor latest_version_list query
pithos: Add new indexes on attributes table
pithos: Add new indexes on nodes table
pithos: Add new indexes on versions table
ui: Break word for images with large names
docs: Remove obsolete Archipelago documentation
docs: Update upgrade guide for 0.16

    - Include Pithos upgrade notes
docs: Update upgrade guide for 0.16

        - Include introduction section
cyclades: Fix small issues with snapshots

* fix IndexError in snf-ganeti-event when processing an
  OP_INSTANCE_SNAPSHOT operation without defining --disk option.
* fix TypeError in snf-dispatcher when processing an
  OP_INSTANCE_SNAPSHOT without snapshot information.

Both issues are caused by using directly the 'gnt-instance snaspshot'
command.
gtools: Make eventd tolerate unhandled exceptions

Make 'snf-ganeti-eventd' daemon tolerate exceptions while processing
events, in order to avoid losing many Ganeti events because of a failure
to process a message of specific type.