[LTP] [PATCH 1/1] tst_test.sh: Fix check for $TST_DEVICE

[Jan Stancek]

----- Original Message -----
> When tst_device acquire call fails, it outputs into stdout,
> therefore the content is actually help message.
> => Check for file presence rather than variable not being empty.
> 
> Fixes: c5ac5d712 tst_test.sh: Make use of tst_device helper
> 
> Signed-off-by: Petr Vorel <pvorel@suse.cz>

Good find, ACK

> ---
> Hi,
> 
> other option would be to check $?.

Or both. Attach is very last call to ioctl(), so I think
we can't end up with valid block device and non-zero retcode.