Tag filtering for skip_tag incorrectly expanded

--skip_tags foo::bar splits the tag on the namespace separator :: and expands to skip the set ['foo::bar', 'foo', 'bar']. Because resources are tagged with all parent tags, this means that every resource in the `foo` namespace is skipped when --skip_tags foo::bar is used. The same expansion issue was addressed for the --tags flag in PUP-4495, but it appears that the expansion logic for --tags and --skip_tags is separate.