Use COMMON_PYPI_MIRROR_URL in discern,ora,edx_ansible,supervisor,xqueue,xserver

Make it easier to use a local pypi mirror in the roles listed above
Add my name to AUTHORS, Wang Peifeng <pku9104038@hotmail.com>
Merge pull request #977 from edx/feanil/local_pypi

Feanil/local pypi