lib/repo-refs: Include remote refs when using collections

lib/repo-refs: Include remote refs when using collections

When working with collections it can be useful to see remote refs rather
than just local and mirrored ones. This commit changes the "ostree refs
-c" output to include remote refs, and includes remote refs with
collection IDs in summary file generation as well. The former behavior
is consistent with how "ostree refs" works, and the latter behavior is
useful in facilitating P2P updates even when mirrors haven't been
configured.

To accomplish this, OstreeRepoListRefsExtFlags was extended with an
EXCLUDE_REMOTES flag. This was done rather than an INCLUDE_REMOTES flag
so that existing calls to ostree_repo_list_refs_ext continue to have the
same behavior. This flag was added to ostree_repo_list_collection_refs
(which is an experimental API break).

Also, add unit tests for the "refs -c" and summary file behavior, and
update relevant tests.

Closes: #1069
Approved by: cgwalters