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

Lustre-change: https://review.whamcloud.com/#/c/34559/
Lustre-commit: fa9922e8f0af3ddadce07aed7d27b00e42f4b487

Change-Id: I9929471abd48b214510bcb499e25793ad120e6d1
Signed-off-by: Gu Zheng <gzheng@ddn.com>
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/34614
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>