The <pkg_name>_pkg variable needs to be set in add_cdat_package_dependent

<pkg_name>_pkg was only set in add_cdat_package(...) however, some
calls to add_cdat_package_dependent(...) never make it into
add_cdat_package(...) so set the variable up in
add_cdat_package_dependent(...) as well.
Pass path the built yasm to ffmpeg build

Ensure ffmpeg uses built version of yasm if we are building it.
Fix package order

Make sure dependent packages are included in the correct order.
WIP: Need to check this change???
Turn off all modules by default

Rely on dependencies to turn on the modules require to support
CDAT and VisTrails.