burnin: Cleanup stale snapshots
burnin: Don't check snapshots' metadata

Function '_get_list_of_sys_images' should not return registered
snapshots.
cyclades: Use X-UA-Compatible meta tag

Using this tag we explicitly set the Compatibility mode for Internet
Explorer to 'Standard'.
admin: Return QuerySet when a filter has no input

If a filter has not been given an input, then django-filter should
normally not call its function. However, it seems this is not the case
with the index Volume filter, whose function is called with no value and
as a result, it returns an empty QuerySet.

Fix this issue by checking in filter_index if it has been passed with
any parameters. Also, since this issue may appear in other filter
functions too, add the same check in every function that doesn't have
it.

NOTE: Model filters have a decorator that automatically does this check
for them.
pithos: Extend backend

Provide an additional backend method 'get_object_by_uuid'
which gets the object's UUID as an input
and return metadata and permission information
about the object.
pithos: PEP8 fixes
pithos: Slight change in get_domain_objects

This method gets two keyword arguments: user and check_permissions.
If check_permissions is True returns only the object accessible to the user.
Otherwise list all the objects for the specific domain ignoring
permissions.
The latter case is only meaningful if user is not provided,
therefore in that case it raises AssertionError.