When non-supported version of python is set as default, Ambari fails in multiple places

We had an issue where the root user's ~/.bashrc file had Python 3 in the PATH.
We blindly tried to execute tasks and hdp-select blew up with a syntax issue.
The vast majority of our tasks will fail with python 3 and as users start to
more heavily adopt newer version of python for data science tasks there is
risk that they will leak into being used by our user accounts, specifically
root for root agents, and the non-root user for non-root agents.
I would propose that we check the version of python before attempting to start
the ambari-agent, and fail with a non-zero exit code if we detect a non-
compliant version.