[thirdparty] minor refactor in build-if-necessary
[thirdparty] minor refactor in build-if-necessary

This commit does a minor refactor in build-if-necessary.sh to always
display informing message when not rebuilding thirdparty.

Change-Id: I2ca2d8907061c1a4ace06a9f624262313a62f700
Reviewed-on: http://gerrit.cloudera.org:8080/11397
Reviewed-by: Adar Dembo <866ca730bfc7f544e3ebce604ceeba4879f23df0@cloudera.com>
Reviewed-by: Dan Burkert <4ef91e292a55314d2653d35ff669a6bd939ce515@apache.org>
Tested-by: Kudu Jenkins

helifu/kudu,InspurUSA/kudu,helifu/kudu,helifu/kudu,InspurUSA/kudu,helifu/kudu,helifu/kudu,InspurUSA/kudu,InspurUSA/kudu,helifu/kudu,helifu/kudu,InspurUSA/kudu,InspurUSA/kudu,InspurUSA/kudu,InspurUSA/kudu,helifu/kudu,InspurUSA/kudu,helifu/kudu