Cover projects missing on the server (incl. `--fail-fast`), missing
project & manifest revisions, and local changes that conflict with an
incoming change. The tests check that repo exits non-zero with a useful
error, leaves the rest of the tree usable, and recovers once the problem
is fixed.
Let `RepoClient.init` return failures instead of raising.
Bug: 566270944
Change-Id: I84e2b8c0bb6012678add77360b446d4bea010c78
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/648548
Reviewed-by: Gavin Mak <gavinmak@google.com>
Tested-by: Brian Gan <brgan@google.com>
Commit-Queue: Brian Gan <brgan@google.com>
