LU-12141 build: correct the required kernel version for lustre kmod

LU-12141 build: correct the required kernel version for lustre kmod

Use %kversion rather than %kver when creating preamble for lustre kmods
in lustre spec, to avoid *Requires kernel version* mismatch.

Test-Parameters: trivial

Change-Id: I9929471abd48b214510bcb499e25793ad120e6d1
Signed-off-by: Gu Zheng <gzheng@ddn.com>
Reviewed-on: https://review.whamcloud.com/34559
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Tested-by: Wang Shilong <wshilong@ddn.com>
Tested-by: Jenkins
Reviewed-by: Li Xi <lixi@ddn.com>
Reviewed-by: Nathaniel Clark <nclark@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>