[#3770] Fix dhcp6_options.modfication_ts

[#3770] Fix dhcp6_options.modfication_ts

Fix dhcp6_options modification_ts column omitted in
original upgrade script and add checks of dhcp6_options changes

/src/bin/admin/tests/mysql_tests.sh.in
    mysql_upgrade_30_to_31_test()
    mysql_migrate_dhcpX_options_client_classes()
    - add dhcp6_options check

/src/bin/admin/tests/pgsql_tests.sh.in
    pgsql_upgrade_29_to_30_test()
    pgsql_migrate_dhcpX_options_client_classes()
    - add dhcp6_options check

/src/share/database/scripts/pgsql/dhcpdb_create.pgsql
    Include conditional add of dhcp6_columns.modification_ts

src/share/database/scripts/pgsql/upgrade_006.2_to_007.0.sh.in
    Add dhcp6_columns.modification_ts

/src/share/database/scripts/pgsql/upgrade_029_to_030.sh.in
    Include conditional add of dhcp6_columns.modification_ts