Repairs to sheet_utils changes, addressing C4-1111 (and C4-1116)

[coveralls]

Pull Request Test Coverage Report for Build 6641737300

• 823 of 919 (89.55%) changed or added relevant lines in 7 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.9%) to 78.558%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
dcicutils/misc_utils.py	37	40	92.5%
dcicutils/validation_utils.py	110	122	90.16%
dcicutils/bundle_utils.py	312	352	88.64%
dcicutils/sheet_utils.py	350	391	89.51%
<!--	Total:	823	919	89.55%	-->

Totals
Change from base Build 6422359319:	0.9%
Covered Lines:	9291
Relevant Lines:	11827

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💛 - Coveralls

[netsettler]

This passed tests at this point. I'm going to re-base it and that may or may not still show.