selftests: Fix loss of test output in run_kselftests.sh

Commit fbcab13d ("selftests: silence test output by default")
changed the run_tests logic as well as the logic to generate
run_kselftests.sh to redirect test output away from the console.

As discussed on the list and at kernel summit, this is not a desirable
default as it means in order to debug a failure the console output is
not sufficient, you also need access to the test machine to get the
full test logs. Additionally it's impolite to write directly to
/tmp/$TEST_NAME on shared systems.

The change to the run_tests logic was reverted in commit
a323335e ("selftests: lib.mk: print individual test results to
console by default"), and instead a summary option was added so that
quiet output could be requested.

However the change to run_kselftests.sh was left as-is.

This commit applies the same logic to the run_kselftests.sh code, ie.
the script now takes a "--summary" option which suppresses the output,
but shows all output by default.

Additionally instead of writing to /tmp/$TEST_NAME the output is
redirected to the directory where the generated test script is
located.

Fixes: fbcab13d ("selftests: silence test output by default")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>