The D2 client configuration parameter, replace-client-name, was
    changed from a boolean, to an enumerated list of modes:

        "NEVER" - do not alter or supply the client name
        "ALWAYS" - always replace the client name, or supply it if
         not sent by the client
        "WHEN_PRESENT" - replace the client name sent by the client,
         do not supply one otherwise
        "WHEN_NOT_PRESENT" - supply the client name only if one was
        not sent by the client

    src/lib/dhcpsrv/d2_client_cfg.cc
    src/lib/dhcpsrv/d2_client_cfg.h
        Added the D2ClientConfig::ReplaceClientNameMode enumeration.

    src/lib/dhcpsrv/parsers/dhcp_parsers.cc
        - Alter replace-client-name parsing to parse the mode labels.
        - Maps boolean literals true and false to RCM_WHEN_PRESENT and
        RCM_NEVER respectively

    src/bin/dhcp4/dhcp6_srv.cc
    src/bin/dhcp4/dhcp4_srv.cc
    src/lib/dhcpsrv/d2_client_mgr.h
        - Adapted to use the enumeration

    src/bin/dhcp4/tests/config_parser_unittest.cc
    src/bin/dhcp4/tests/fqdn_unittest.cc
    src/bin/dhcp6/tests/config_parser_unittest.cc
    src/bin/dhcp6/tests/fqdn_unittest.cc
    src/lib/dhcpsrv/tests/cfgmgr_unittest.cc
    src/lib/dhcpsrv/tests/d2_client_unittest.cc
    src/lib/dhcpsrv/tests/d2_udp_unittest.cc
    src/lib/dhcpsrv/tests/dhcp_parsers_unittest.cc
        - Alter existing tests to use the enumeration. Note false was replaced
        with RCM_NEVER and true with RCM_WHEN_PRESENT