More manifest_repo work

Added RepairManifestsOnDisk function and necessary support functions.

BUG=chromium:980346
TEST=run_tests.sh

Change-Id: I80146f4150888310f3cf0992072ed78d555fc9b0
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/go/+/1699897
Commit-Queue: Jack Neus <jackneus@google.com>
Tested-by: Jack Neus <jackneus@google.com>
Reviewed-by: Sean Abraham <seanabraham@chromium.org>
Reviewed-by: Evan Hernandez <evanhernandez@chromium.org>
5 files changed