This is an attempt to allow people to change the default configuration
to try harder at 'mounting' a tape. This allows you to specify, in
seconds, the amount of time a non-control unit open will retry
(once per second) the scsipi_test_unit_ready when it tries to mount
the tape. It also turns off the over-verbose error reporting at
this time unless SCSIDEBUG is set.
The reason this is not enabled as a default is that it's a large change
of behaviour. I find it useful to 'try harder' at mounting a tape in
the tape driver, particularly when loaded via a media changer device
rather than specifying the delays in the backup program.