Galaxy: Map python -> python3 (make it standard)
Galaxy: Map python -> python3 (make it standard)

Some calls Galaxy makes (like running pysam.bcftools.index) are
directly called using subprocess. As these commands are simply
called using `python -c ...` this results in Galaxy using Python2
by accident, result in the error:

> ImportError: No module named pysam.bcftools

Linking the `python` command to Python3 fixes this.

chambm/docker-galaxy-stable,bgruening/docker-galaxy-stable,bgruening/docker-galaxy-stable,chambm/docker-galaxy-stable,bgruening/docker-galaxy-stable,chambm/docker-galaxy-stable