WL#2856: Use scripts to cover more test cases

Current NDB testing:

1) mysql-test, via mysqld
   - fixed tables and test cases (SQL)
   - single-threaded
   - no NDB restart testing

2) autotest, via C programs
   - fixed single tables and test cases (NDB API)
   - multi-threaded, presses NDB to the limit
   - tests NDB node and system restarts

It seems useful to add a third type, mainly to cover
more cases:

3) perl test scripts, via dbi:mysql
   - variable tables and test cases (SQL)
   - multi-threaded
   - can do NDB restarts
   - can look "outside" e.g. to verify local files

Variable tests can mean random, or exhaustive when possible.
The script itself will verify results by computing them.

Multi-threading, unlike in 2) is not for pressing NDB on
a single table, but to run parallel ops on different tables
to find "global variable" problems in NDB.

Implementation-wise there should be a file of perl modules
(support for sql, mgm, etc) and the test scripts themselves.

The scripts should be runnable standalone or via 1) and 2)
using a welldefined way to pass environment and parameters.