Add test for --remote-only option too

Also changed notation of symlink stuff from dst/src to path/target, because I get really confused by dst/src!

By setting them to empty string

Add more unit tests

This filters out all redundant matches, i.e. matches that are subpaths
of other matches (except for the std symlink dirs - we need to return
these as we need to follow their targets).

As was implemented in a previous commit, it still also filters out
subpaths of symlinks as we don't want to follow symlinks (again except
for the std symlink dirs).

Add unit tests

Do not retry a failed clean on an install target using the next platform in the list if the remote clean command failed due to a non-SSH reason (if ret code != 255).