[#3463] Added v6 implementation

[#3463] Added v6 implementation

/src/bin/dhcp6/dhcp6_srv.cc
    Dhcpv6Srv::processLocalizedQuery6() - add response6 to leases6_committed
    callout arguments

/src/bin/dhcp6/tests/hooks_unittest.cc
    Update tests to expect with response6

/src/hooks/dhcp/lease_cmds/lease_cmds.*
    Add leases6Committed() handler

/src/hooks/dhcp/lease_cmds/lease_cmds_callouts.cc
    Add leases6_committed()callout

/src/hooks/dhcp/lease_cmds/lease_cmds_messages.mes
    LEASE_CMDS_LEASES6_COMMITTED_FAILED - new message

/src/hooks/dhcp/lease_cmds/tests/lease_cmds6_unittest.cc
    TEST_F(Lease6CmdsTest, validLeases6Committed)
    TEST_F(Lease6CmdsTest, validLeases6CommittedMultiThreading)
    TEST_F(Lease6CmdsTest, nopLeases6Committed)
    TEST_F(Lease6CmdsTest, nopLeases6CommittedMultiThreading)
    - new tests