Bug 4317: Added the version of yang-maven-plugin.
Bug 4317: Added the version of yang-maven-plugin.

In the pom.xml of config-parent, the version of yang-maven-plugin was
missing. In the result, Maven downloaded the latest release version
(0.7.1-Lithium-SR1) of yang-maven-plugin, although the latest SNAPSHOT
version (0.8.0-SNAPSHOT) was expected here.
This patch added the version of yang-maven-plugin, and specified the
latest SNAPSHOT version for it.

Change-Id: I9a30aa4fc3c80d81c9342664135be484a219493d
Signed-off-by: Hideyuki Tai <87b3ecc686f9d387127fb9c6b83e75a0e66a7ae8@necam.com>

inocybe/odl-controller,inocybe/odl-controller,Sushma7785/OpenDayLight-Load-Balancer,522986491/controller,opendaylight/controller,522986491/controller,Johnson-Chou/test,Johnson-Chou/test,Sushma7785/OpenDayLight-Load-Balancer