Python3 support

[oliver-tarrant-tessella]

Trying to run a python job with python version = 3 fails with a message in the logs + pyv3='/opt/entrypoint.sh: line 80: python3: command not found'. It appears that python3 is not installed in our spark image. This should be changed by editingpiezo/Spark/Dockerfile to ensure that python3 jobs can be run.

Acceptance criteria:

• [x] Can run jobs using python 3
• [x] Python 2 jobs still run

Test Scenarios in addition to Acceptance criteria scenarios:

• [x] Python 3 job complete successfully
• [x] A user-friendly error message displayed when Py-3 job fails

[vidhyamanojkumar]

Language input is case sensitive. "language":"python", doesn't work, whereas Python works fine. This issue applies to Scala too.

[robert-clegg-tessella]

The options for "language" are clearly documented in the User guide on the wiki.