Adds lease-dump to kea-admin.  While merging, additonal changes
were needed:

src/bin/admin/tests/mysql_tests.sh.in
 mysql_wipe() - functio was failing referential integrity checks
 due to new tables added in schema 3.0.  Was deleting all
 tables except "hosts".  This has been fixed.

Added src/bin/admin/scripts/mysql/lease_dump_3.0.sh