add repohooks

By default, no hooks are enabled, so this shouldn't impact people.

Bug: 28295071
Test: `repo upload` in a repo didn't blow up

Change-Id: I46a8476f7eaef80e68d9e7b3cc46741267150b67
1 file changed
tree: 87c82e1a8142ddce17fe00f340da42a55ab41e5f
  1. default.xml