* Updated vm provisioning scripts to build and install P4Runtime
Also, hardcoded commit ID for each tool to improve reproducibility
of exercises (the P4Runtime API could change in the future).
TODO: there is a permission error at line 114 of user-bootstrap.sh that
needs to be fixed.
* Removed unnecessary compiler flags when bulding PI
* Fixed permission error and updated BMv2 and PI commit IDs
* Created new subdirectory for Fall developer day.
* Created vm directory for P4D2_2017_Fall. Fixed emacs permission problem.
* Remove checkout of SIGCOMM branch.
