Allow assigning code ownership to all users

By using '*' as email the code ownership can be assigned to all users.
This effectively exempts the owned files from requiring code owner
approvals since a code owner approval of the patch set uploader is
always implict and if all users are code owners uploaded changes are
always implicitly approved.

Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: I187a6f99e71819b3fc801d3314c20020ef02d26f