LU-12511 build: ignore kmod handling in spec file for

LU-12511 build: ignore kmod handling in spec file for
 utilities only build

The lustre spec file handles kmod even when --disable-modules is
used. We don't need to manage any kmod in this case so lets make
that handling only when ${with lustre_modules} is true.

Test-Parameters: trivial
Change-Id: Ifa43720aacabae5f41abf250d2e03b235c34cb4c
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/38649
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Nathaniel Clark <nclark@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>