The mysqltest command "real_sleep" is an old artifact from early
days of MySQL development, it no longer serves any purpose.

  SELECT * FROM t1;
  --sleep 3
  SELECT * FROM T1

The intention was that one should be able write tests using the sleep
command and if the machine is slow, pass --sleep with a higher value
in order to increase the time slept during the test. This is not
practical in an automated test environment like we have today.

Using "mysqltest --sleep 1", the above sleep would be changed to 1
second and "mysqltest --sleep=10" would change it to 10 seconds.
If there are more sleep commands in a test, they will all be changed
to same value and hence, it doesn't scale.

We have already changed all usage of sleep into loops and there are
various include files to use to wait until certain condition has been
fulfilled. This has made it possible to run our test suite on both
slow and fast machines.

The patch does the following :-
- Removes the mysqltest "real_sleep" command. All instances of the
  command in the test suite are replaced with the "sleep" command.
- Removes the "mysqltest --sleep" command line argument.
- Removes the "mysql-test-run.pl --sleep" command line argument.
- Changes the mysqltest "sleep" command to always wait as long as
  argument specified.
- Updates the code comments for "do_sleep()" to indicate that
  fractional values can be used as a sleep value, not only whole
  seconds. i.e., sleep 0.1;
- Updates the mysqltest documentation to delete all information about
  the removed command and options. It also clearly describes that the
  "sleep" command supports sleeping for intervals which are less than
  one second.

Change-Id: I060d635aa3cbcb62323d1e5ea946264a44a56461