Add a lot more owners to testing/buildbot/OWNERS.

R=phajdan.jr@chromium.org, sky@chromium.org

Review URL: https://codereview.chromium.org/543323002

Cr-Commit-Position: refs/heads/master@{#293982}

testing/buildbot/OWNERS

 # This is needed because of * in testing/OWNERS .
+# This is reserved for people that are comfortably with buildbot recipes
+# and understand the implications of changing these files.
 set noparent
 
+cmp@chromium.org
 darin@chromium.org
+dpranke@chromium.org
+jam@chromium.org
+jochen@chromium.org
+machenbach@chromium.org
 phajdan.jr@chromium.org
 sky@chromium.org