WIP: petsc4py build ported to Ubuntu

I keep needing to waggle the petsc.yaml file around.  Once I've got something working on SageMathCloud I'll synthesize the working builds I've got on OS X, Ubuntu, SLES, and SMC into a single petsc.py configurator.  

* Uses host BLAS and LAPACK packages
* (Untrustworthy host MPICH build)