FIX: fixes regressions introduced in #984

Various fixes on previous pull request:

- Fixed a non tested case: single service override.
- Fixed `resource_macros_names` attribute definition in `Config` class. It was declared as `StringProp`, but this attribute is a list object. This mislead the multi valued attribute processing that returned the last list element rather than the list itself. Also removed the last uncecessary `[]` on the `_echo` command definition.
- Also fixed `test_properties_defaults.py` modified in #979