Use current user ID on calls to CAF::FileWriter

When unit testing, UID won't be 0, so use $< instead.
Use $$ for current PID in cmdfile and flagfile

Add support for $$ in cmdfile and flagfile and use this to make the
filenames unique when unit testing.
Continue if resource path does not exist

The merge_pkg_paths() method should continue if a named resource path
does not exist, rather than causing an LC exception.
Add end-to-end tests of Configure() entry point