[4202] Replaced underscores with hypens in NCR JSON element names

[4202] Replaced underscores with hypens in NCR JSON element names

The NCR element names have also been changed to use hyphens.  This touched
quita a few unit tests. Files modified:

    src/bin/d2/tests/d2_process_unittests.cc
    src/bin/d2/tests/d2_queue_mgr_unittests.cc
    src/bin/d2/tests/d2_update_mgr_unittests.cc
    src/bin/d2/tests/nc_add_unittests.cc
    src/bin/d2/tests/nc_remove_unittests.cc
    src/bin/d2/tests/nc_test_utils.cc
    src/bin/d2/tests/nc_trans_unittests.cc
    src/bin/dhcp4/tests/d2_unittest.cc
    src/bin/dhcp6/tests/d2_unittest.cc
    src/lib/dhcp_ddns/libdhcp_ddns.dox
    src/lib/dhcp_ddns/ncr_msg.cc
    src/lib/dhcp_ddns/tests/ncr_udp_unittests.cc
    src/lib/dhcp_ddns/tests/ncr_unittests.cc
    src/lib/dhcpsrv/tests/d2_udp_unittest.cc