Don't crash if the connection has an error

Fixes crahses associated to

    File "/usr/local/lib/python2.7/dist-packages/paramiko-1.15.1-py2.7.egg/paramiko/transport.py", line 731, in     open_channel
        raise e
    error: [Errno 104] Connection reset by peer


    !!! ERROR - Oops! Looks like you've found a bug in StarCluster
    !!! ERROR - Crash report written to: /home/datacratic/.starcluster/logs/crash-report-9893.txt
    !!! ERROR - Please remove any sensitive data from the crash report
    !!! ERROR - and submit it to starcluster@mit.edu