Add comment about using relative paths for expr_mgmt's outdir.
First pass at getting regression suite working with cmake build process.

The documentation has been updated too. Now, no mention of autotools is
done when talking about PLFS. Instead, it is only mentioned in
conjunction with building MPI and that they correct version of autotools
is expected to already be accessible in the environment.
Update make command to include verbose output.
Fix for ad_plfs build when not building PLFS