GitLab

- added --with-kea-config=JSON,BIND10 added to configure.ac
- JSON-file config backend added for b10-dhcp6
- Config file can now be read from a JSON file

Replaced use of internal queue in Dhcpv6Srv with posting
NCRs to D2ClientMgr. Upgraded unit tests accordingly.
b10-dhcp6 is now fully able to participate in DDNS.

Added D2ClientMgr send mode control and error handler
to Dhcp6vSrv and use of each to ControlledDhcpv6Srv.
Added new unit test files d2_unittest.h and cc.

Replaced logic in Dhcpv6Srv::generateFqdn() which constructed the
FQDN from the lease address to use D2ClientMgr::generateFqdn() method.
Removed remaining obsolete FQDN_ constants.

Also, allow the server to generate FQDN if configured to do so, even if
client specified non-empty FQDN.

Also added spaces around some operators.

Added the ChangeLog entry and fixed a minor clang complain in dhcp6.