dashboard/app: properly and consistently show git tree/commit

[dvyukov]

Request by Alan Stern on a mailing list:
https://lore.kernel.org/all/Yc5rgUo8dyJKX98M@rowland.harvard.edu/

We tried to make info in reports more concise and tidy by saying "upstream" instead of full git repository and used only 8 characters from commit hash to fit more of the commit subject:

HEAD commit:    b51594df Merge tag 'docs-5.9-3' of git://[git.lwn.net/linux](http://git.lwn.net/linux)
git tree:       upstream

The problem is that we don't accept back in patch testing requests "upstream" as a valid git repository, so users can't copy-paste. The proposal is to not abbreviate and always spell full git repository.
8 characters is considered too short, 12 characters is the standard length.

Need to audit all places we show git repositories and commit hashes.

[a-nogikh]

From an offline discussion: an alternative approach is to actually let patch testing recognize such aliases.

[a-nogikh]

8 characters is considered too short, 12 characters is the standard length.

We currently print 12 chars for bug reports and 8 for patch testing requests. I'll update that a bit later -- now we have two pending PRs that affect dashboard, I fear there might be some conflicts if I add the third one.