archipelago: Do not rename a mapped volume
mapper: Change volume state to OPENING earlier

Mark volume as opening before starting open procedure. This implicitly marks the
volume as not ready, so if the open procedure blocks for any reason (e.g. there
are no available xseg reqeusts), then any subsequent operation on the same
volume will have to wait until the volume becomes ready.
mapper: Fix count of map nodes when preparing I/O
mapper: Add map purge functionality
mapper: Fix delete map data state

Add delete map data state and use it when appropriate
mapper: Add delete map handling function
mapper: Add DESTROYING map state
mapper: Use delete map function when destroying volume

Use the generic delete map function when destroying a volume. Also use the
approriate map state.
mapper: Add seperate key field to maps

Add seperate key filed to maps, to be used for cache indexing purposes.
mapper: Use the new key field when caching map
mapper: Add change volume target functionality for maps
mapper: Introduce seperate get_ready_map function

When loading a resource, use a new seperate get_ready_map function to simplify
the process.
mapper: Refactor rename function

Add seperate rename function and make rename code path use it
mapper: Use fallback map with the 'archip_' prefix

If loading a map with its name fails, try falling back to the volume prefixed by
'archip_'. Then, if this succeeds and we have exclusive access to the map, to a
permanent rename to get rid of the archip prefix.

The above is needed to fasciliate live volume migrations to the new naming
scheme.
mapper: Use purge when renaming 'archip_' maps
vlmc: Disallow creating volumes starting with 'archip_'

Since the 'archip_' prefix was used to differentiate archipelago from pithos
objects, keep it reserved and do not allow creating resources with this prefix.
vlmc: Drop the old prefix when manually handling locks
mapper: Return error if map cannot be inserted to cache
mapper: Remove excessive logging on map node references
mapper: Fix number of object of uninitialized maps