selftest/cases/glibc.py: increase the memory for testing

Some of the tests trigger OOM and fail. Increase the amount of memory
available so we dont run into these issues.

Signed-off-by: Anuj Mittal <anuj.mittal@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 4d22dba4)
Signed-off-by: Steve Sakoman <steve@sakoman.com>