Fix circular lookup when AS cert not found.

[kormat]

Fixes #3194

This also changes the logic for determining if the trust store is
authoritative or not for a given query. The rules are:

• A CS is authoritative for its own certs for its own AS.
• A core CS is authoritative for all AS certs in the local ISD.
• A core CS is authoritative for TRCs for the local ISD.

Also:

• Make logging/errors a bit more consistent/useful in getChain.

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This change is 

[oncilla]

Reviewed 2 of 2 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved

[oncilla]

Reviewable status: complete! all files reviewed, all discussions resolved

[oncilla]

Reviewed 2 of 2 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved

[oncilla]

Reviewed 1 of 1 files at r3.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @kormat)

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go/lib/infra/modules/trust/trust.go, line 226 at r3 (raw file):

		// XXX(kormat): Wrap ErrMissingAuthoritative with ErrNotFoundLocally to
		// simplify logic in LoadAuthoritativeTRC
		return nil, serrors.Wrap(ErrNotFoundLocally,

Why not serrors.Wrap(ErrNotFoundLocally, ErrMissingAuthoritative, "isd"...) ?

[oncilla]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @kormat)

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go/lib/infra/modules/trust/trust.go, line 226 at r3 (raw file):

Previously, Oncilla wrote…

Why not serrors.Wrap(ErrNotFoundLocally, ErrMissingAuthoritative, "isd"...) ?

Or rather the other way around: serrors.Wrap(ErrMissingAuthoritative, ErrNotFoundLocally, "isd"...)

[oncilla]

Reviewed 1 of 1 files at r4.
Reviewable status: complete! all files reviewed, all discussions resolved

[oncilla]

Reviewable status: complete! all files reviewed, all discussions resolved