systemd-nspawn: decrease non-fatal mount errors to debug level (syste…

…md#4569)

non-fatal mount errors shouldn't be logged as warnings.
(cherry picked from commit bdb4e0c)

[tblume: fixes bsc#1004289]

src/nspawn/nspawn-mount.c

@@ -435,7 +435,7 @@ int mount_all(const char *dest,
                                 o = options;
                 }
 
-                r = mount_verbose(mount_table[k].fatal ? LOG_ERR : LOG_WARNING,
+                r = mount_verbose(mount_table[k].fatal ? LOG_ERR : LOG_DEBUG,
                                   mount_table[k].what,
                                   where,
                                   mount_table[k].type,