Use python2 to build and run MysticMine.

PEP-394 defines that python2 should point to the system's python >= 2 installation, and python3 to the system's python >= 3.

Since many systems nowadays use python3 as the default python (ie: python is a symlink to python3), python2 should explicitly be specified when python < 3 is required.

This pull request updates the build scripts, and MysticMine to use python2 by default, since it's dependecies don't yet work on python3.

Specifically, it'll make MysticMine work unpatched on systems/distributions that use python3 by default.