GitLab

- cppcheck issues
- Unique index for prefix and prefix length.

- Added new table host_identifier_type
- Added foreign key on hosts table referencing
  host_identifier_type
- Indexes on hosts table are now unique

- Rename GET_HOST_HWADDR_DUID to GET_HOST_DHCPID
- Fixes and clarifications in doxygen documentation

The updated API exposes functions which retrieve hosts
by any identifier and identifier type, rather than DUID
or HW address.

Committing on my discretion and with no objections on jabber.

Also, use new constant for checking fetch failure in MySQL.

- Introduced constants for MySQL fetch results
- Simplified loops in generic SQL unit tests
- Removed some typos
- Removed unused variables

 - addressed most review comments
 - added new unit-tests
 - remove reservation for temporary addresses TA
 - updated AUTHORS file

 - Tomek verified that it applied cleanly, compiled and
   unit-tests passed.

fixes:
mysql_host_data_source.cc:236:33: error: invalid conversion from 'size_t* {aka unsigned int*}' to 'long unsigned int*' [-fpermissive]
                 bind_[1].length = &dhcp_identifier_length_;
                                 ^
mysql_host_data_source.cc:243:33: error: invalid conversion from 'size_t* {aka unsigned int*}' to 'long unsigned int*' [-fpermissive]
                 bind_[1].length = &dhcp_identifier_length_;
                                 ^
mysql_host_data_source.cc:344:25: error: invalid conversion from 'size_t* {aka unsigned int*}' to 'long unsigned int*' [-fpermissive]
         bind_[1].length = &dhcp_identifier_length_;

src/lib/dhcpsrv/dhcpsrv_messages.mes
    Added hosts database specific messages

src/lib/dhcpsrv/host_data_source_factory.cc
src/lib/dhcpsrv/mysql_host_data_source.cc
    Updated log statements with hosts database messages

 - Includes fix in AllocEngine6Test ctor, provided by Thomas

# Conflicts:
#	src/lib/dhcpsrv/mysql_lease_mgr.cc
#	src/lib/dhcpsrv/mysql_lease_mgr.h