LU-15286 build: only use baseonly option on el7

LU-15286 build: only use baseonly option on el7

el7 baseonly option allow to build perf package while
in el8 does not.

Lustre-change: https://review.whamcloud.com/45677
Lustre-commit: 6eb5d3ae4aaab1662afc8ae50f56b0a0eaa6556a

Change-Id: Ie973c5cc816b4b98ef71ab7080bd11286bcd644a
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/46056
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>