Make build system more flexible for testing

Update the cvmix_setup script to allow the compiler and netCDF location to be
passed in from the command line, and update to the Bryan-Lewis regression test
to allow the test to run without rebuilding the executable (if this works
nicely in the testing framework, I'll extend to the rest of the tests).

Updating all the testing scripts makes me wonder if I should
(a) modularize the testing framework (keep in bash or move to python?)
(b) run both the pointer and memcopy branches of Bryan-Lewis in the same script
    (much like the KPP test has 6 subtests that all get run)