doc/guide/ctrl-channel.xml
    Added libreload to common command section

src/bin/dhcp4/ctrl_dhcp4_srv.cc
    Registered and deregistered libreload command

src/bin/dhcp4/tests/ctrl_dhcp4_srv_unittest.cc
    TEST_F(CtrlChannelDhcpv4SrvTest, libreload) - modified to
    test using CommandMgr instance

src/bin/dhcp6/ctrl_dhcp6_srv.cc
    Registered and deregistered libreload command

src/bin/dhcp6/tests/ctrl_dhcp6_srv_unittest.cc
    TEST_F(CtrlChannelDhcpv6SrvTest, libreload) - modified to
    test using CommandMgr instance