Make MPI an option to disable.

On BGAS, running with MPI linked causes the RDMA network devices to
become unusable, unless the (non-mpi) application is run through mpirun
:-/

Also remove non-leaky SKV dependency.
Merge branch 'master' of https://github.com/eile/Lunchbox
Merge branch 'master' of https://github.com/Eyescale/Lunchbox
Delay print of log legend to first output
Merge pull request #174 from eile/master

Delay print of log legend to first output