libostree v2018.8

[Colin Walters <walters verbum org>]

https://github.com/ostreedev/ostree/releases/tag/v2018.8

This release is pretty much all minor bugfixes: memory leaks,
fixing error messages and docs, handling a race condition
on pull with summary updates.  There's one new feature (noted below),
and we also gained a new contributing tutorial:
https://mail.gnome.org/archives/ostree-list/2018-August/msg00005.html
Thanks to Robert Fairley and Cheryl Fong!

The one bugfix I want to call out explicitly is:
  ostree-remount.service: RemainAfterExit=yes 
PR: #1697
It's surprising it took us so long to find and fix this; I've seen
occasional boot failures that I believe trace down to this problem.
The behavior of systemd units of Type=simple without RemainAfterExit=yes set
is rather nonsensical; I may try to push to have a warning emitted
upstream if such a unit is a dependency of another.

And the one new feature is the `auto-update-summary` config option
for repositories.  For more information, see the docs and
PR: #1681

Thanks to all contributors!

```
Alexander Larsson (3 PRs, 3 commits)
  Fix leak in ostree_repo_list_collection_refs (#1700)
  ostree_repo_static_delta_generate: Fix leak (#1701)
  ostree_repo_pull_from_remotes_async: Fix leak of options (#1702)

Colin Walters (3 PRs, 3 commits)
  lib/pull: Fix minor memleak in error path (#1684)
  ostree-remount.service: RemainAfterExit=yes (#1697)
  Release 2018.8 (#1705)

Dan Nicholson (1 PR, 5 commits)
  PR: #1698
    repo: Add OSTREE_REPO_TEST_ERROR=invalid-cache env var
    tests: Test for recovery from corrupted summary cache
    lib/pull: Fetch summary if cached version doesn't match signature
    lib/pull: Add debug message when loading summary from cache
    tests: Add tests for remote summary update races

Jonathan Lebon (4 PRs, 10 commits)
  ci: Bump rpm-ostree tag we build for tests (#1708)
  PR: #1692
    lib: Fix some logic/error-checking code
    lib: Fix some minor memory leaks
    lib: Check for NULL pointers in some more places
  PR: #1693
    lib/commit: Only auto-update summary if refs were written
    lib/config: Deprecate commit-update-summary option
    lib/config: Rename change-update-summary to auto-...
    lib/refs: Use GLNX_HASH_TABLE_FOREACH_KV helper
  PR: #1710
    ostree/config: Delete rogue printf and tweak help
    man/config: Keep cmdsynopsis for GROUP.KEY version

Matthew Leeds (4 PRs, 5 commits)
  man/ostree.repo-config: Update min-free-space-* docs (#1687)
  lib/repo-commit: Fix min-free-space error message (#1691)
  lib/repo-pull: Use correct keyring for dynamic remotes (#1695)
  PR: #1681
    config: Add a core/change-update-summary option
    lib/repo: Take exclusive lock while generating summary

Philip Withnall (1 PR, 1 commit)
  lib/repo-pull: Prefer object pull over from-scratch delta if ref exists (#1709)

Robert Fairley (2 PRs, 2 commits)
  docs: Add Contributing Tutorial to Mkdocs pages (#1711)
  PR: #1694
    docs: Add contributing tutorial
    (and 1 commit from other author)

Sinny Kumari (1 PR, 1 commit)
  src/ostree: Add --group option to ostree config (#1696)

Stefan Agner (1 PR, 1 commit)
  Avoid race condition in case tests directory does not exist (#1704)

Umang Jain (1 PR, 1 commit)
  Post-release version bump (#1683)

Will Thompson (1 PR, 1 commit)
  repo: remove outdated note from write_config() docs (#1707)

Will Thompson (1 PR, 1 commit)
  man/ostree.repo-config: improve min-free-space-* docs (#1706)

bubblemelon (2 PRs, 2 commits)
  bin/refs: Clarify --create error message (#1690)
  PR: #1694
    docs: Add detail to CONTRIBUTING.md and link to tutorial
    (and 1 commit from other author)
```