new resolve method and tests
 new resolve method most calls to var_list.get_str,  var_list.resolve_string replaced with  var_list.resolve.
* New resolve methods for ConfigVarList: resolve, resolve_to_list, replace previous methods: get_str, resolve_string get_list.
* Tests for new resolve methods.
* Removed unused member Configvar.__resolving_in_progress, preventing circular resolves is done in ConfigVarList.
* Replaced all previous resolve methods with resolve, resolve_var, resolve_to_list, resolve_var_to_list.
removed redundant resolve
merged branch shai, new resolve alg and methods