mysqlslap: setting --engine does not get replicated
    http://bugs.mysql.com/bug.php?id=46967

and
    mysqlslap: specifying --engine and --create does not
    work with --engine=<storage_engine>:<option>
    https://bugs.launchpad.net/maria/+bug/429773

Problems were that an --engine=<storage_engine> was translated
to a "set storage_engine = <storage_engine>", wich is _not_
replicated. A --engine=<storage_engine>:<option> was not always
properly parsed and in some cases crashed.

Fixed by eliminating "set storage_engine = ..." and adding
proper DDL generation. Initialized an unitialized buffer to
prevent crashes and fixed to use proper pointer for in
case of --engine=<storage_engine>:<option> being the last
element in list of --engines.

Also cleaned up code for better readability.

Q: Should MySQL's replication actually replicate a
   "set storage_engine = ..." command or not?
A: No it should not. It is documented here:
   http://dev.mysql.com/doc/refman/5.1/en/replication-features-variables.html
   ...
   "The storage_engine system variable is not replicated, which is a
   good thing for replication between different storage engines." ...

Before the patch, mysqlslap was behaving this way:

+-------------------------------+--------+-------------+
|                               | single | replication |
+-------------------------------+--------+-------------+
| Before patch                                         | 
+-------------------------------+--------+-------------+
| --engine[1]                                          |
+-----+-------------------------+--------+-------------+
| 1.1 | eng1                    |  OK    |   Not OK    |
| 1.2 | eng1,eng2               |  OK    |   Not OK    |
| 1.3 | eng1,eng2,eng3          |  OK    |   Not OK    |
| 1.4 | memory:option           |  OK    |   Not OK    |
| 1.5 | memory:option,eng1      |  OK    |   Not OK    |
| 1.6 | eng1,memory:option      | Not OK |   Not OK    |
| 1.7 | memory:option,eng1,eng2 | Crash  |   Not OK    |
| 1.8 | eng1,memory:option,eng2 |  OK    |   Not OK    |
| 1.9 | eng1,eng2,memory:option | Not OK |   Not OK    |
+-----+-------------------------+--------+-------------+
+-------------------------------+--------+-------------+
| --create --engine[2]                                 |
+-----+-------------------------+--------+-------------+
| 2.1 | eng1                    |  OK    |   Not OK    |
| 2.2 | eng1,eng2               |  OK    |   Not OK    |
| 2.3 | eng1,eng2,eng3          |  OK    |   Not OK    |
| 2.4 | memory:option           | Not OK |   Not OK    |
| 2.5 | memory:option,eng1      | Not OK |   Not OK    |
| 2.6 | eng1,memory:option      | Not OK |   Not OK    |
| 2.7 | memory:option,eng1,eng2 | Crash  |   Not OK    |
| 2.8 | eng1,memory:option,eng2 | Not OK |   Not OK    |
| 2.9 | eng1,eng2,memory:option | Not OK |   Not OK    |
+-----+-------------------------+--------+-------------+

After my final patch, mysqlslap now runs like this:

+-------------------------------+--------+-------------+
|                               | single | replication |
+-------------------------------+--------+-------------+
| After third patch                                    | 
+-------------------------------+--------+-------------+
| --engine[1]                                          |
+-----+-------------------------+--------+-------------+
| 1.1 | eng1                    |  OK    |  OK         |
| 1.2 | eng1,eng2               |  OK    |  OK         |
| 1.3 | eng1,eng2,eng3          |  OK    |  OK         |
| 1.4 | memory:option           |  OK    |  OK         |
| 1.5 | memory:option,eng1      |  OK    |  OK         |
| 1.6 | eng1,memory:option      |  OK    |  OK         |
| 1.7 | memory:option,eng1,eng2 |  OK    |  OK         |
| 1.8 | eng1,memory:option,eng2 |  OK    |  OK         |
| 1.9 | eng1,eng2,memory:option |  OK    |  OK         |
+-----+-------------------------+--------+-------------+
+-------------------------------+--------+-------------+
| --create --engine[2]                                 |
+-----+-------------------------+--------+-------------+
| 2.1 | eng1                    |  OK    |  OK         |
| 2.2 | eng1,eng2               |  OK    |  OK         |
| 2.3 | eng1,eng2,eng3          |  OK    |  OK         |
| 2.4 | memory:option           |  OK    |  OK         |
| 2.5 | memory:option,eng1      |  OK    |  OK         |
| 2.6 | eng1,memory:option      |  OK    |  OK         |
| 2.7 | memory:option,eng1,eng2 |  OK    |  OK         |
| 2.8 | eng1,memory:option,eng2 |  OK    |  OK         |
| 2.9 | eng1,eng2,memory:option |  OK    |  OK         |
+-----+-------------------------+--------+-------------+