Added High-Performance Linpack (HPL) example.

Requires passing in the size of matrix to test, as well as the location
of the xhpl binary for the test platform.  Optionally, can set the parallelism
for each run of HPL as well.  See hpl.py --help for more information.

Outstanding issues:
- Need ability to express parameters as logscaled by a particular base
- Some parameters are encoded as integers but should really be switches