LU-16382 config: ensure lutf.sh is included in dist

LU-16382 config: ensure lutf.sh is included in dist

The official 2.15.1 source distribution does not contain
lutf.sh.  As lustre.spec lists it (when LUTF is enabled) this causes a
build error.

It is likely not included because "./configure --enable-dist" was run
in a context where swig was not installed.

So when determining whether to enable lutf, first check for
enable_dist and in the case for enable_lutf="yes"

Test-Parameters: trivial
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: If5f856985a6d642822baba4b6ee301c04f851217
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/49382
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Cyril Bordage <cbordage@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>