[thirdparty] add license info about yaml-cpp and chrony
[thirdparty] add license info about yaml-cpp and chrony

Added license information on yaml-cpp and chrony (build/test-only
dependency) into thirdparty/LICENSE.txt.

This patch doesn't have any functional modifications.

Change-Id: I65dfaa917fdf4f0831471b3e730bf8be19ebdc2d
Reviewed-on: http://gerrit.cloudera.org:8080/14637
Tested-by: Kudu Jenkins
Reviewed-by: Alexey Serbin <864f6b82bd94e8dda64141d4274519ee66e0102e@cloudera.com>

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