[#3858] Skip ping-check if active or reserved

[#3858] Skip ping-check if active or reserved

/src/bin/dhcp4/dhcp4_srv.cc
    Dhcpv4Srv::processLocalizedQuery4() - pass in current host to callout

/src/bin/dhcp4/tests/hooks_unittest.cc
    Update UTs to check for host argument

/src/hooks/dhcp/ping_check/ping_check_callouts.cc
    lease4_offer() - pass host argument to PingCheckMgr::shouldPing()

/src/hooks/dhcp/ping_check/ping_check_mgr.*
    PingCheckMgr::shouldPing() - added host parameter and altered
    logic to skip ping if lease is active or reserved

/src/hooks/dhcp/ping_check/tests/ping_check_mgr_unittests.cc
    Updated UTs