[5586] Added schema unit tests

[5586] Added schema unit tests

src/share/database/scripts/mysql/upgrade_5.2_to_6.0.sh.in
    Added SQL statements to populate lease4/6_stat tables
    from existing lease table content.

src/bin/admin/tests/dhcpdb_create_5.1.mysql
    New file used for upgrade testing

src/bin/admin/tests/mysql_tests.sh.in
    run_statement() - new convenience function for running SQL
    statements with an optional expected return value

    mysql_lease4_stat_test() - verifies lease4_stat
    table and trigger operations on a new database

    mysql_lease6_stat_test()
    mysql_lease6_stat_per_type() - new functions
    which lease6_stat table and trigger operations
    on a new database

    mysql_lease_stat_upgrade_test() - new function
    which verifies data migration from an earlier
    schema and trigger operation