BACKPORT: ltp and kselftests: Add owners

Add Betty and Joe to OWNERS for ltp and kselftests.

Test: N/A
Signed-off-by: Edward Liaw <edliaw@google.com>
(cherry picked from https://android-review.googlesource.com/q/commit:98abbe018d05ac37f691a39999932bce4fb5e6af)
Merged-In: Id8123dd2aeb849fdb334f018754902e2f245f1c3
Change-Id: Id8123dd2aeb849fdb334f018754902e2f245f1c3
[edliaw: created OWNERS file and also added vmartensson, edliaw, and balsini]