autotest_quickmerge: fix breakage in building autotest-tests
autotest_quickmerge: fix breakage in building autotest-tests

Instead of making quickmerge-created files be owned by autotest-tests
(an arbitrary choice), make them owned by autotest. This ensures that
they are properly unmerged before tests are built.

BUG=chromium:239631
TEST=While cros working on autotest-tests, do a `autotest_quickmerge
--board={board}`, then do a `build_packages`. Build no longer fails.
Same applies when working on `autotest`, or `autotest-chrome`.

Change-Id: I3c1df56c5b504f01594de14aa4c5bdaa7d8b1e8d
Reviewed-on: https://gerrit.chromium.org/gerrit/50749
Tested-by: Aviv Keshet <178e8ae417efbe404feca7ab4cb8f0ba8c109369@chromium.org>
Reviewed-by: Chris Masone <98e3d65c6b0e9e2391eb4c2e8b1e572b77e544ed@chromium.org>
Commit-Queue: Aviv Keshet <178e8ae417efbe404feca7ab4cb8f0ba8c109369@chromium.org>

bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite,bpsinc-native/src_third_party_chromite,bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite