Iterate through modules directly

Instead of iterating through groups and then iterating through the
group's modules, iterate through the modules directly.  This will
allow circular dependencies between groups as long as the individual
modules don't have circular dependencies.  In order to maintain the
ordering of modules in a group, each module is considered to have
an implicit dependency on any earlier modules in the same group.

Change-Id: Ibce67167c7234db70ede0a6b5c2b43fb8e0bb05d