A call to HooksManager::getHooksManager().unloadLibraries() was added to
the destructors Dhcpv4Srv::~Dhcpv4Srv() and Dhcpv6Srv::~Dhcpv6Srv(). This
ensures hook libraries are unloaded prior to static objects.

- No additional check for HR mode in findReservations
- Additional commentary in the loop collecting host ids.

    Merges in trac4239.

This change was suggested during a ticket review.

src/lib/dhcpsrv/pgsql_lease_mgr.cc
    Amended commentary for getColumnValue() variants
    Added decription of Uiaid union
    Changed std::system to ::system

src/lib/dhcpsrv/testutils/mysql_schema.cc
    Changed std::system to ::system

src/lib/dhcpsrv/testutils/mysql_schema.h
    Fixed typo

src/lib/dhcpsrv/testutils/pgsql_schema.cc
    Removed extraneous include
    Changed std::system to ::system

Both DHCPv4 and DHCPv6.

The identifiers are held on an ordered list and the server will
use them to search for host reservations for each client using
this order.

    Moved schema scripts into a new common location:

        src/share/database/scripts

    to make them accessible to both kea-admin and dhcpsrv testing

Added Angelo as contributor.

Rather than use hard-coded lists or query logic for dropping the
database all MySQL and Posgresql tests use new drop scripts
added to src/bind/admin/scripts.

src/bin/admin/scripts/mysql/dhcpdb_drop.mysql
    - New SQL script to drop a MySQL database

src/bin/admin/scripts/pgsql/dhcpdb_drop.pgsql
    - New SQL script to drop a Postgresql database

src/bin/admin/tests/mysql_tests.sh.in
    - mysql_wipe() - modified to use new drop script

src/bin/admin/tests/pgsql_tests.sh.in
    - pgsql_wipe() modified to use new drop script

src/lib/dhcpsrv/tests/mysql_lease_mgr_unittest.cc
    - TEST(MySqlOpenTest, OpenDatabase) - added show_err=true
    to destroyMySQLSchema() calls

src/lib/dhcpsrv/tests/pgsql_lease_mgr_unittest.cc
    - TEST(PgSqlOpenTest, OpenDatabase) - added show_err=true
    to destroyMySQLSchema() calls

src/lib/dhcpsrv/testutils/mysql_schema.cc
    - destroyMySQLSchema(bool show_err) - modified to use the new
    drop script and accept show_err parameter

src/lib/dhcpsrv/testutils/pgsql_schema.cc
    - destroyPgSQLSchema(bool show_err) - modified to use the new
    drop script and accept show_err parameter

src/lib/dhcpsrv/testutils/schema.h
src/lib/dhcpsrv/testutils/schema.cc
    New files that contain constants and functions common to RDBMS
    testing

src/lib/dhcpsrv/testutils/pgsql_schema.h
src/lib/dhcpsrv/testutils/pgsql_schema.cc
    New files that contain constants and functions needed for
    Posgresql testing

src/lib/dhcpsrv/testutils/mysql_schema.cc
src/lib/dhcpsrv/testutils/mysql_schema.h
    Removed common constants and functions
    Added MYSQL_VALID_TYPE
    runMySQLScript() - new function to submit a script to MySQL

src/lib/dhcpsrv/pgsql_lease_mgr.cc
    PgSqlLease6Exchange - replaced uint32_t iaid member with Uiaid union
    instance.  This permits the value to be safely stored in the database
    as an INT (signed 4-byte value)
    getColumnValue()- added int32_t variant of this method

src/lib/dhcpsrv/tests/Makefile.am
    Removed schema_pgsql_copy.h

src/lib/dhcpsrv/tests/mysql_host_data_source_unittest.cc
src/lib/dhcpsrv/tests/mysql_lease_mgr_unittest.cc
    Altered tests to use MYSQL_VALID_TYPE

src/lib/dhcpsrv/tests/pgsql_lease_mgr_unittest.cc
    Moved constants and functions testutils/pgsl_schema.h & cc

src/lib/dhcpsrv/tests/generic_lease_mgr_unittest.cc
   - GenericLeaseMgrTest::testLease6HWTypeAndSource() - now uses valid values
     for hardware address source

src/lib/dhcpsrv/tests/mysql_lease_mgr_unittest.cc
    TEST(MySqlOpenTest, OpenDatabase) - pass in show_err=true for call
    to createMySQLSchema()

src/lib/dhcpsrv/testutils/Makefile.am
    - Added definition of TEST_ADMIN_SCRIPTS_DIR
    - removed schema_mysql_copy.h

src/lib/dhcpsrv/testutils/mysql_schema.cc
    - Removed include of schema_mysql_copy.h
    - destroyMySQLSchema() - now contains destroy_statment[] formerly
    defined in schema_mysql_copy.h
    - createMySQLSchema() - Creates the database through command line
    invocation of MySQL cli, mysql, passing it the production database
    creation script

    Merges in trac4259.