[OFIWG-MPI] creation of github ofiwg project

[Hefty, Sean]

For those who weren't at the OFIWG F2F, an ofiwg github project was created and the libfabric/fabtests git trees were moved from openfabrics.org to github.

https://github.com/ofiwg/libfabric.git

Github provides better support for a collaborative development effort.  We still anticipate using the openfabrics.org server to host tarballs.

- Sean