As described in issue #44, setting pex_binary's interpreter parameter to
python3 isn't enough, b/c the pex_wrapper will use the same python version that was used to
build pex_wrapper.pex, which is the same as the host machine
/usr/bin/env python. To fix this, we can use PEX_PYTHON environment variable,
which force pex to run pex_wrapper.pex to the specified version
pointed by that environment variable.
As described in issue #44, setting pex_binary's
interpreterparameter to python3 isn't enough, b/c the pex_wrapper will use the same python version that was used to build pex_wrapper.pex, which is the same as the host machine/usr/bin/env python. To fix this, we can usePEX_PYTHONenvironment variable, which force pex to run pex_wrapper.pex to the specified version pointed by that environment variable.