[4316] Changed primary lease event logging from DEBUG to INFO

[4316] Changed primary lease event logging from DEBUG to INFO

src/bin/dhcp4/dhcp4_messages.mes
    - Replaced the word "debug" with "informational" where appropriate

src/bin/dhcp4/dhcp4_srv.cc
    - Changed several lease4_logger messages from DEBUG to INFO
    DHCP4_INIT_REBOOT
    DHCP4_LEASE_ADVERT
    DHCP4_LEASE_ALLOC
    DHCP4_RELEASE
    DHCP4_DECLINE_LEASE

src/bin/dhcp6/dhcp6_messages.mes
    - Replaced the word "debug" with "informational" where appropriate

    - Added two new messages:
    DHCP6_LEASE_RENEW
    DHCP6_PD_LEASE_RENEW

src/bin/dhcp6/dhcp6_srv.cc
    - Changed several lease6_logger messages from DEBUG to INFO
    DHCP6_LEASE_ADVERT
    DHCP6_LEASE_ALLOC
    DHCP6_PD_LEASE_ADVERT
    DHCP6_PD_LEASE_ALLOC
    DHCP6_RELEASE_NA
    DHCP6_RELEASE_PD
    DHCP6_DECLINE_LEASE

    - Dhcpv6Srv::extendIA_NA() - added new log for DHCP6_LEASE_RENEW
    - Dhcpv6Srv::extendIA_PD() - added new log for DHCP6_PD_LEASE_RENEW