mapperd: Support X_TRUNCATE operation
archipelago: Implement volume listing
archipelago: Remove obsolete '-u' option

Remove obsolete '-u' option from Archipelago cli. Since there is no kernel space
part, all Archipelago interactions affect only userspace components.

Using the new blktap infrastructure, during restarts all mapped volumes are
"paused". This allows us to safely perform a full Archipelago restart.
The administrator cannot stop Archipelago when mapped volumes exist, unless the
new '--force' flag is used.
archipelago: Remove obsolete '--pool' argument
vlmc: Validate volume names

Validate volume names. Disallow all volumes:
 * Starting with 'archip_'
 * Ending in '_lock'
 * Ending in '_(hex number){16}'