image.bbclass: Empty /var/volatile if it is a mount point
If /var/volatile is a mount point it shouldn't contain any files before
mount time. If files are there, they will no longer be able to be accessed
once the tmpfs gets mounted at /var/volatile.
This problem can be seen for instance when systemd creates
/var/volatile/log/journal as part of its package installation. It then
assumes the journal is persistent even though /var/volatile/log/journal
goes away shortly thereafter.
This change makes sure that there are no files in /var/volatile if it is
to be used as a mount point.
[Yocto #7388]
Signed-off-by: Randy Witt <randy.e.witt@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
