c2bcfa71f4
For Linux, place a file in the mount point folder so it will be considered "busy". Fix the while loop so it doesn't rm in directories above the testdir. Add Linux-specific code to test overlay on|off. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Paul Zuchowski <pzuchowski@datto.com> Closes #4990 Closes #8081