t/zbd: skip tests that need too many sequential zones

t/zbd: skip tests that need too many sequential zones

Test cases #3, #4, #28, #29 and #48 require rather large numbers of
sequential zones to run properly and they fail if the test target
device has not enough of such zones in its zone configuration.

Check how many sequential zones are present on the test device and
skip any test cases for which this number is not enough.

Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>