Add release groups for building groups of boards.
Add release groups for building groups of boards.

This CL just adds some new groups, but does not use them. They can be
used for testing.

The boards are grouped according to the reference boards mentioned at
http://goto.google.com/cros-names. Only x86 / amd64 boards are grouped.
Only a subset of the boards have been grouped.

BUG=chromium:348226
TEST=Full trybot run of atom-release-group.
TEST=Dump config and verify this change only adds configs, and does not
     modify any existing configs.
TEST=cbuildbot_config_unittest.py

Change-Id: I331d410506f28b6362c11c157efec299543613a6
Reviewed-on: https://chromium-review.googlesource.com/189388
Reviewed-by: Aviv Keshet <178e8ae417efbe404feca7ab4cb8f0ba8c109369@chromium.org>
Commit-Queue: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>
Tested-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@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