volatile-binds: Remove workdir if OverlayFS fails

volatile-binds: Remove workdir if OverlayFS fails

To fulfill OverlayFS workdir requirements, the mount-copybind script
creates a workdir. But if the mount operation fails for any reason,
the workdir is left there.

Then, subsequent runs of mount-copybind will again try to
create the directory and pollute system logs with failed mkdir error
messages.

This commit mitigates the problem by unconditionally removing workdir
if the OverlayFS is not used or fails to run.

Signed-off-by: Ricardo Simoes <ricardo.simoes@pt.bosch.com>
Signed-off-by: Mark Jonas <mark.jonas@de.bosch.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>