tmpfiles: log at info level when some allowed failures occur
    
    In provision.conf we ship:
    
    d- /root :0700 root :root -
    d- /root/.ssh :0700 root :root -
    
    These are allowed to fail, for example on a read-only filesystem. But they still
    log at error level, which is annoying and gets flagged. Tune those specific errors
    down to info.
    
    There are likely more that could be tuned down, but the important thing is to cover
    the tmpfiles.d that we ship right now.
    
    Before:
    
    $ echo -e "d- /root :0700 root :root - \nd- /root/.ssh :0700 root :root -" | SYSTEMD_LOG_LEVEL=err build/systemd-tmpfiles --root=/tmp/img --create -
    Failed to create directory or subvolume "/tmp/img/root": Read-only file system
    Failed to open path '/tmp/img/root': No such file or directory
    $
    
    After:
    
    $ echo -e "d- /root :0700 root :root - \nd- /root/.ssh :0700 root :root -" | SYSTEMD_LOG_LEVEL=err build/systemd-tmpfiles --root=/tmp/img --create -
    $
    
    (cherry picked from commit 244c2a8344c01e94cd9bdf835de998b89bc53179)