[ADAM-1999] Support Python 3

[akmorrow13]

Fixes #1999

[akmorrow13]

Jenkins, test this please.

[coveralls]

Coverage remained the same at 79.25% when pulling d60af8a on akmorrow13:python3 into 43d0595 on bigdatagenomics:master.

[coveralls]

Coverage remained the same at 79.25% when pulling 87d8985 on akmorrow13:python3 into 43d0595 on bigdatagenomics:master.

[AmplabJenkins]

Test FAILed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/ADAM-prb/2836/

Build result: FAILURE

[...truncated 3 lines...]Building remotely on amp-jenkins-worker-05 (centos spark-test) in workspace /home/jenkins/workspace/ADAM-prbWiping out workspace first.Cloning the remote Git repositoryCloning repository https://github.com/bigdatagenomics/adam.git > git init /home/jenkins/workspace/ADAM-prb # timeout=10Fetching upstream changes from https://github.com/bigdatagenomics/adam.git > git --version # timeout=10 > git fetch --tags --progress https://github.com/bigdatagenomics/adam.git +refs/heads/:refs/remotes/origin/ # timeout=15 > git config remote.origin.url https://github.com/bigdatagenomics/adam.git # timeout=10 > git config --add remote.origin.fetch +refs/heads/:refs/remotes/origin/ # timeout=10 > git config remote.origin.url https://github.com/bigdatagenomics/adam.git # timeout=10Fetching upstream changes from https://github.com/bigdatagenomics/adam.git > git fetch --tags --progress https://github.com/bigdatagenomics/adam.git +refs/pull/:refs/remotes/origin/pr/ # timeout=15 > git rev-parse origin/pr/2070/merge^{commit} # timeout=10 > git branch -a -v --no-abbrev --contains b4107fc # timeout=10Checking out Revision b4107fc (origin/pr/2070/merge) > git config core.sparsecheckout # timeout=10 > git checkout -f b4107fc8777251b2b4890d2d6eaeec4a873b8814First time build. Skipping changelog.Triggering ADAM-prb ? 2.7.3,2.11,2.2.2,ubuntuTriggering ADAM-prb ? 2.6.2,2.11,2.2.2,ubuntuADAM-prb ? 2.7.3,2.11,2.2.2,ubuntu completed with result FAILUREADAM-prb ? 2.6.2,2.11,2.2.2,ubuntu completed with result FAILURENotifying endpoint 'HTTP:https://webhooks.gitter.im/e/ac8bb6e9f53357bc8aa8'
Test FAILed.

[AmplabJenkins]

Test PASSed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/ADAM-prb/2837/
Test PASSed.

[akmorrow13]

@heuermh ping for review

[akmorrow13]

@heuermh rebased

[AmplabJenkins]

Test PASSed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/ADAM-prb/2840/
Test PASSed.

[heuermh]

Thank you, @akmorrow13