selftests/resctrl: Change a few printed messages

Change a few printed messages to report test progress more clearly.

Add a missing "\n" at the end of one printed message.

Suggested-by: Shuah Khan <shuah@kernel.org>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>