allow specifying cluter spark version in ec2 script; some PEP changes
allow specifying cluter spark version in ec2 script; some PEP changes

broxtronix/thunder,j-friedrich/thunder,kcompher/thunder,jwittenbach/thunder,pearsonlab/thunder,thunder-project/thunder,zhwa/thunder,mikarubi/thunder,kunallillaney/thunder,j-friedrich/thunder,oliverhuangchao/thunder,zhwa/thunder,broxtronix/thunder,pearsonlab/thunder,kunallillaney/thunder,mikarubi/thunder,oliverhuangchao/thunder,poolio/thunder,poolio/thunder,kcompher/thunder