suzerain: #3122 add --drive3hbl option

Overrides default 3D behavior of disabling driving forces
on homogenized boundary layer problems so that I can "jolt"
a drifting condition back to match desired freestream state.

Added because I'm seeing unpleasant, appreciable drift in
freestream temperatures.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@45359 0bd85f0b-c151-43b9-a1e9-27231104551f