Pg_upgrade failed - what does "re-initdb" mean?
The error means that the failed upgrade has left /var/lib/postgresql/9.3/main/ in an unusable state, broken and half upgraded. To attempt to upgrade again you must first remove it, then re-create it by running initdb like you did to create it the first time.

Look at pg_upgrade_dump_27132.log and pg_upgrade_server.log to see why the upgrade failed. Re-running it without changing anything is not likely to make any difference.