selftests: settings: tests can be in subsubdirs

Commit 852c8cbf ("selftests/kselftest/runner.sh: Add 45 second
timeout per test") adds support for a new per-test-directory "settings"
file. But this only works for tests not in a sub-subdirectories, e.g.

 - tools/testing/selftests/rtc (rtc) is OK,
 - tools/testing/selftests/net/mptcp (net/mptcp) is not.

We have to increase the timeout for net/mptcp tests which are not
upstreamed yet but this fix is valid for other tests if they need to add
a "settings" file, see the full list with:

  tools/testing/selftests/*/*/**/Makefile

Note that this patch changes the text header message printed at the end
of the execution but this text is modified only for the tests that are
in sub-subdirectories, e.g.

  ok 1 selftests: net/mptcp: mptcp_connect.sh

Before we had:

  ok 1 selftests: mptcp: mptcp_connect.sh

But showing the full target name is probably better, just in case a
subsubdir has the same name as another one in another subdirectory.

Fixes: 852c8cbf

 (selftests/kselftest/runner.sh: Add 45 second timeout per test)
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>