[reconciler] Skip on Live Balance Fetch Errors at Tip

[patrick-ogrady]

It is possible that the reconciler could query an account balance at an index not known to a Rosetta implementation if any balance queries are made before the syncer processes a node re-org. This PR ensures we treat these as "skipped" reconciliations instead of failures.

If a failure occurs because of some re-org (and we are querying balance at an index ahead of tip), we will retry the skipped reconciliation when the balance changes from the replacement blocks are added.

Changes

• Add IndexAtTip to ReconcilerHelper
• Skip reconciliation if balance fetch fails at tip
• Add IndexAtTip to BlockStorage

[coveralls]

Pull Request Test Coverage Report for Build 10459

• 72 of 80 (90.0%) changed or added relevant lines in 2 files are covered.
• 3 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.09%) to 78.93%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
reconciler/reconciler.go	43	47	91.49%
storage/block_storage.go	29	33	87.88%

Files with Coverage Reduction	New Missed Lines	%
storage/block_storage.go	1	75.0%
reconciler/reconciler.go	2	83.4%

Totals
Change from base Build 10368:	0.09%
Covered Lines:	7215
Relevant Lines:	9141

---

💛 - Coveralls

[arjun-io]

Couple of non-blocking nits