In a recent PR, we changed the provider requirements code to permit
per-module requirements gathering, to enhance the provider command
output. This had an incorrect implementation of recursive requirements
gathering for the normal case, which resulted in only depth-1 modules
being inspected.
This commit fixes the broken recursion and adds a grandchild module to
the unit tests as test coverage. This also demanded fixing the
testNestedModuleConfigFromDir helper function to cope with nested
modules in test configs.
45f7da9678