WL#6731: Switch default engine to innodb in MTR

Problem Statement
-------------------
MySQL 5.5 changed the default storage engine from MyISAM to innodb . A change in
storage engine has a big impact on the test suite. All the
result files would change and lot of investigation is required to validate the
new result files. In order to avoid changing the test suite it was decided to
change MTR instead to start the server with MyISAM as the default.

As a result of the above change the main MySQL functional test suite is running
with MyISAM as the storage engine and test coverage on innodb is limited. Even
the new tests and suites continue to run with MyISAM unless the tests
specifically mention innodb as the storage engine

Goal
------
The goal of this WL is to change MTR such that it starts the server with Innodb
unless MyISAM explicitly specified in the test

Requirements
--------------

R01 - MTR by default should start the server with the default storage engine, innodb
R02 - The existing tests that do not explicitly specify any engine should
continue to run with MyISAM until the result files are migrated to innodb 
R03 - Existing tests that explicity specify an engine should continue to run
with the specified engine
R04 - All suites and tests added to MTR after wl6731 have been pushed to trunk
should run with the default storage engine of the server unless the test
explicitly specifies another storage engine
R05 - Tests that specify engine=innodb when creating tables, should no longer do
that since it is now redundant, unless the tests runs the server with another
engine as default

The code in the above branch has the following changes:

1. The default MyISAM has been changed to Innodb in mtr, the change can be found 
in mtr_cases.pm
2. All existing test cases except the ones that run Innodb has been changed to 
use 
MyISAM, a new quote

# "This line and the line below is a temporary line for tests that do not need 
MyISAM in future, but 
need to be kept for tests that need it.\n--source 
include/force_default_myisam.inc" -- 
has 
been added to test 
cases.

3. A new file  include/have_myisam.inc in source for future use and is empty.
   A new empty file include/force_default_myisam.inc has been added to be 
included in tests that require MyISAM.

 The idea is to keep the quote in point 2 for test cases which is still running 
MyISAM and remove it 
when it moves to Innodb, for test cases which will be running MyISAM even in 
future needs to keep this 
line.


R01 - MTR by default should start the server with the default storage engine, 
innodb

  R01 has been satisfied.

R02 - The existing tests that do not explicitly specify any engine should
continue to run with MyISAM until the result files are migrated to innodb 

  R02 satisfied.
R03 - Existing tests that explicity specify an engine should continue to run
with the specified engine

 R03 satisfied.
 
RO4 - All new suites and tests should run with innodb unless the test explicitly
specifies that it should run with another storage engine.
 
 R04 satisfied.