[5705] AllocEngine4 now matches clients to global HRs

[5705] AllocEngine4 now matches clients to global HRs

src/bin/dhcp4/tests/Makefile.am
src/bin/dhcp4/tests/host_unittest.cc - new file with global HR tests

src/lib/dhcpsrv/alloc_engine.*
    findGlobalReservation() - new function that searches for global HR

    findReservation() - calls findGlobalReservation() if mode is global

    hasAddressReservation()
    ClientContext4::currentHost()
        - modified to recognize global HRs

src/lib/dhcpsrv/network.h
    Added new mode, Netork::HR_GLOBAL

src/lib/dhcpsrv/tests/alloc_engine4_unittest.cc
    TEST_F(AllocEngine4Test, globalReservationReservedAddressDiscover)
    TEST_F(AllocEngine4Test, globalReservationReservedAddressRequest)
    TEST_F(AllocEngine4Test, globalReservationDynamicDiscover)
    TEST_F(AllocEngine4Test, globalReservationDynamicRequest) - new tests