zbd/007: Reset test target zones at test end

zbd/007: Reset test target zones at test end

The test case zbd/007 checks write pointer mapping between a logical
device and its container device. To do so, it moves write pointers of
the container device by writing data to the container device. When the
logical device is a dm-crypt device, this test case works as expected,
but the data written to the container device is not encrypted, then it
leaves broken data on the logical, dm-crypt device. This results in I/O
errors in the following operations to the dm-crypt device.

To avoid the I/O errors, reset the test target zones of the logical
device at the test case end to wipe out the broken data.

Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>