log: introduce new helper call log_setup_service()

Let's reduce the common boilerplate and have a single setup function
used by all service code to setup logging.

src/cryptsetup/cryptsetup.c

@@ -609,9 +609,7 @@ int main(int argc, char *argv[]) {
                 goto finish;
         }
 
-        log_set_target(LOG_TARGET_AUTO);
-        log_parse_environment();
-        log_open();
+        log_setup_service();
 
         umask(0022);