convert pmdk/pmemobj pools to a newer on-memory format

 The on-memory format of data pools used by libpmemobj is not compatible
 between major releases, and the library doesn't currently support automatic
 conversion. Such upgrades need to be done manually, by this tool.
 .
 This version supports formats of PMDK up to 1.7. Upgrades to any prior
 version are supported as well, but no downgrades.