Clean up return code types

* Remove dds_return_t / dds_retcode_t distinction (now there is only
  dds_return_t and all error codes are always negative)

* Remove Q_ERR_... error codes and replace them by DDS_RETCODE_...
  ones so that there is only one set of error codes

* Replace a whole bunch "int" return types that were used to return
  Q_ERR_... codes by "dds_return_t" return types

Signed-off-by: Erik Boasson <eb@ilities.com>

src/core/ddsc/tests/config.c

@@ -49,7 +49,7 @@ static void config__check_env(
         }
 
         if ( !env_ok ) {
-            dds_retcode_t r;
+            dds_return_t r;
 
             r = ddsrt_setenv(env_variable, expected_value);
             CU_ASSERT_EQUAL_FATAL(r, DDS_RETCODE_OK);