D2ClientMgr functions now get behavior parameters from a passed in
structure instead of D2ClientMgr::d2_client_config_.

src/lib/dhcpsrv/d2_client_cfg.h
    struct DdnsParams  - new structure to convey request specific
    (i.e.scopable) Ddns params

src/lib/dhcpsrv/alloc_engine.cc
src/lib/dhcpsrv/alloc_engine.h
    Added ddns_params_ to ClientContext4/6

src/lib/dhcpsrv/d2_client_mgr.*
    D2ClientMgr::adjustFqdnFlags()
    D2ClientMgr::adjustDomainName()
    D2ClientMgr::analyzeFqdn()
    D2ClientMgr::generateFqdn()
    D2ClientMgr::qualifyName() - now accept DdnsParams instance as
    parameter

src/lib/dhcpsrv/tests/d2_client_unittest.cc
    Reworked tests to use DdnsParams