Fix problem with short max extension
Shell Program Error. Exit status: 7 'nobody nobody webmanage_instance -t 465f0b690aa31874a75639b64a1ccaa3 -- extend 6611b04d-f4af-11e7-b222-90e2ba22fee4 -f /tmp/extensionpSlmQQ -e '2018-01-13T00:00:00Z' '72''
Calling POSIX::tmpnam() is deprecated at /usr/testbed/lib/APT_Instance.pm line 2331. Failed to extend slice at wisc.cloudlab.us: Extension refused by reservation system: Insufficient free nodes at Fri Jan 12 19:00:00 2018 (2 more needed).