BUG-1914: force maven 3.1.1
BUG-1914: force maven 3.1.1

Activates maven version enforcement.

Change-Id: I19bbd53e93de3ccbf029a2e029e479217e2c0c09
Signed-off-by: Robert Varga <b8bd3df785fdc0ff42dd1710c5d91998513c57ef@cisco.com>

522986491/yangtools,opendaylight/yangtools,NovusTheory/yangtools,opendaylight/yangtools