LU-11946 build: no yaml check during configure --enable-dist

LU-11946 build: no yaml check during configure --enable-dist

If the yaml libraries are not found, the error is fatal, and prevents
the sources from being packaged.

This check is unnecessary when sources are being packaged, so this patch
disables the test when configure is run with --enable-dist.

Lustre-change: https://review.whamcloud.com/34812
Lustre-commit: 748ede308d0eb2bb2762cae9c45978808e20a735

Change-Id: I160e0d54efc59480d2f830607467dbc9f34c9de3
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Reviewed-by: Nathaniel Clark <nclark@whamcloud.com>
Reviewed-by: Minh Diep <mdiep@whamcloud.com>
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/35088
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>