Bump yangtools dependency to 1.2.0
Bump yangtools dependency to 1.2.0

Issue: RELENG-485
Change-Id: I597e7f907b5a327084fb570f24bf436bee7f5eb5
Signed-off-by: Thanh Ha <09ea4d3a79c8bee41a16519f6a431f6bc0fd8d6f@linuxfoundation.org>

opendaylight/packetcable,opendaylight/packetcable