Implements disk space monitoring for the JEB backend, import and rebuild operations.
When low disk space is threshold is reached, the operation will abort and close the environment cleanly. All indexes will be left in the "untrusted" state so the user knows the DB is invalid. It will also print the appropriate message depending on which import phase when the threshold is reached: * phase 1 failure: import append + replace required to continue. * phase 2 failure: rebuildAll required to continue.