Ignore ErrCanceled errors returned by verifyState

[bartekn]

What version are you using?

What did you do?

Horizon shutdown during state verification.

What did you expect to see?

No errors.

What did you see instead?

WARN[2020-02-04T18:14:19.987+01:00] State verification errored                    err="addAccountsToStateVerifier failed: Error running history.Q.GetAccountsByIDs: select failed: context canceled" pid=99452 service=expingest

Looks like we should add similar condition like in:

go/services/horizon/internal/expingest/main.go

Lines 238 to 246 in 6af401e

	if cause := errors.Cause(err); cause != nil &&
	cause != context.Canceled &&
	cause != db.ErrCancelled {
	log.WithFields(logpkg.F{
	"error": err,
	"current_state": cur,
	"next_state": next.node,
	}).Error("Error in ingestion state machine")
	}

Seems like it's a simple fix but we're going to release beta really soon so adding to stable milestone.