eddy_cpu command is called twice - once with --nthr=1, and again with --nthr=8

machine. Save runEddy output to file so we can inspect it on failures

code is shared across all tests in a common "runEddy" script. Also test both
$FSLDIR/bin/eddy_openmp and $FSLDIR/bin/eddy_cpu if either exist.

FEAT analysis

The random element of running GPS is taken out by using precomputed gradient orientations.
The old implementation set a random subset of bvecs to b=0 (or to b=2000).
This is now fixed ensuring that the full bvecs are used for each shell.