Fixes a non tested case: single service override.
Fixed Config's `resource_macros_names` definition.

The `resource_macros_names` in the `Config` class 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.
Fixed test_properties_defaults.py modified in #979
Merge pull request #989 from geektophe/fix_single_service_override

FIX: fixes regressions introduced in #984