tree-wide: fix a number of log calls that use %m but have no errno set

This is mostly fall-out from d1a1f0aaf0,
however some cases are older bugs.

There might be more issues lurking, this was a simple grep for "%m"
across the tree, with all lines removed that mention "errno" at all.

src/shared/bus-unit-util.c

@@ -1156,8 +1156,10 @@ static int bus_append_execute_property(sd_bus_message *m, const char *field, con
                         r = extract_first_word(&w, &path, ":", EXTRACT_DONT_COALESCE_SEPARATORS);
                         if (r < 0)
                                 return log_error_errno(r, "Failed to parse argument: %m");
-                        if (r == 0)
-                                return log_error("Failed to parse argument: %m");
+                        if (r == 0) {
+                                log_error("Failed to parse argument: %s", p);
+                                return -EINVAL;
+                        }
 
                         r = sd_bus_message_append(m, "(ss)", path, w);
                         if (r < 0)

src/shared/conf-parser.c

@@ -303,8 +303,8 @@ int config_parse(const char *unit,
                         /* Only log on request, except for ENOENT,
                          * since we return 0 to the caller. */
                         if ((flags & CONFIG_PARSE_WARN) || errno == ENOENT)
-                                log_full(errno == ENOENT ? LOG_DEBUG : LOG_ERR,
-                                         "Failed to open configuration file '%s': %m", filename);
+                                log_full_errno(errno == ENOENT ? LOG_DEBUG : LOG_ERR, errno,
+                                               "Failed to open configuration file '%s': %m", filename);
                         return errno == ENOENT ? 0 : -errno;
                 }
         }

src/shared/dropin.c

@@ -210,7 +210,7 @@ static int unit_file_find_dirs(
 
         type = unit_name_to_type(name);
         if (type < 0) {
-                log_error("Failed to to derive unit type from unit name: %m");
+                log_error("Failed to to derive unit type from unit name: %s", name);
                 return -EINVAL;
         }