Fix the 15_create_smallmem_pos.py test, which was failing because the

Fix the 15_create_smallmem_pos.py test, which was failing because the
set console.limit command in the test was never being run. The select in
Console.py was never timing out because there was always someting to read on
the fd, the OOM messages are constant. So the test would hang.

The fix includes:

1) Changing MEM in 15_create_smallmem_pos.py to 32MBs, which is the default
   for the tools that should work.
2) Change the XmConsole init to add an argument to set the console limit
   when it's created.
3) Set a default large limit for console so we won't hang in the future.
4) Added a new 16_create_smallmem_neg.py test to handle failure situation.
5) Added comment in README.

Signed-off-by: Daniel Stekloff <dsteklof@us.ibm.com>