msgctl11: cleanup and fflush removed

Performed some cleanup and removed fflush() from the
testcase.

fflush() before FORK_OR_VFORK() is not needed because of
commit 3f0510cb2d18720e294e89fbdb4ce38e0ede47d6

fflush() before exit() is redundant.

Signed-off-by: Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>
msgctl11: process message queues by portions

/proc/sys/kernel/msgmni value scales with the amount of the host memory.

On systems with several tens gigabytes of ram this value is rather big (and
even may reach its limit - IPCMI (32768), defined in include/linux/ipc.h) and
therefore the test case fails with "Not enough free pids" error.

Now we process all avaliable message queues by portions (with the size based
on the amount of free pids).

Signed-off-by: Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>