mapper: Introduce map signature

Introduce map signature to identify archipelago maps. The signature is 4 bytes
long and represents the string "AMF."

If the signature is not matched, then if the mapper identifies the mapfile as
version 1, it proceeds. Otherwise, we rely upon a user provided assume_v0 flag
to interpret the mapfile as a Pithos (version 0) mapfile. Moreover, mapper now
implicitly and automatically upgrades the version 0 mapfiles to the latest
version.

Also, mapper does not implicitly creates separate namespaces for archipelago
and Pithos maps (version 0) by default. So the "archip_" prefix is not inserted
for objects that represent  map data or volume data.
mapper: Automatically flag zero objects on v0 read
mapper: Support creating maps from an object list
Python: Add support for the new X_CREATE op
tests: Do not expect objects with the "archip_" prefix
tests: Add tests for the new X_CREATE operation
Python: remove obsolete cont_addr option in clone
vlmcd: Propagate v0 info to mapper requests
mapper: Delete map data when deleting a map

Delete map data when deleting a map, instead of only marking it as deleted.

Enhance map functions with a delete_map_data method. Implement it for all
supported versions (v2) and provide stubs for the rest (v0, v1).
mapper: Add support for map renaming.

Support map renaming functionality. It is currently implemented as the
equivalent of a copy and a delete functionality.

The current implementations is problematic, if the user attempts to rename a
mapped volume from the node on which it is mapped. In that case, the rename will
proceed and the mapped volume will experience I/O errors.

The solution to the above problem is not trivial and will be addressed in future
commits.
python: Add support for the rename request
tests: Add tests for the rename functionality
Archipelago: add vlmc rename functionality

Add rename functionality to the vlmc client along with the provided userspace
management tool.
mapper: Fix flags when creating new maps
archipelago: Extend v0 options to vlmc api
archipelago: Extend v0 options to the cli application
archipelago: Pass v0 options to blktap
mapper: Add MF_OBJECT_DELETED flag

Keep track of deleted objects on the mapfile, by setting the aforementioned flag
when deleting an object.
mapper: Add object delete functionality

Add mapper handling functions to delete an object. Also provide an appropriate
callback function.
mapper: Remove unused objects on removal

Remove unused objects on resource removal. These writable archipelago objects
are certainly garbage, so we can remove them eagerly when removing a resource.