include buildtool_export_depends explicitly with run_depends

When generating architecture specific packages for Debian and Fedora we need to include the `buildtool_export_depends` (empty if package.xml version == 1) with the `run_depends`.

The `buildtool_export_depends` should not be included into `run_depends` implicitly like `build_export_depends` and `exec_depends` are in `catkin_pkg.package.Package`, but instead should only be used in this particular packaging case.