fix unit test for pkg/scaffold/internal

[howieyuen]

TestTemplateRepository_Templates

UT read from subdir means to fetch 2 or more templates from pkg/scaffold/internal, now we have only one template, which is not compatible with more templates in the future.

TestCopyTemplateFiles

The flaw of this one is pretty the same as above. Copy templates from src dir to target dir, now src dir contains only one, so it's not compatible with more templates as well.

[coveralls]

Pull Request Test Coverage Report for Build 2473968440

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 5 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.06%) to 75.837%

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Files with Coverage Reduction	New Missed Lines	%
pkg/scaffold/external_templates.go	2	69.86%
pkg/engine/operation/parser.go	3	85.19%

Totals
Change from base Build 2467368842:	-0.06%
Covered Lines:	3691
Relevant Lines:	4867

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💛 - Coveralls

[elliotxx]

Need to supplement PR description

[elliotxx]

lgtm

[markliby]

lgtm