Add mode bits to open() with O_CREAT.

If you call open() with O_CREAT, you need to pass a third argument to
open; see http://man7.org/linux/man-pages/man2/open.2.html .

We're trying to (re-)introduce checks that will turn open calls like
these into compile-time errors, but in order to do that, we need to
clean up all existing instances of this kind of code.

Bug: None.
Test: Still builds. m test-art-host-gtest-profile_assistant_test passes.
Change-Id: Ia754999a30cfc01c0826c69687b33c09884aea6d