Upgrade: check systemvm template before db changes#4582

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yadvr merged 3 commits intoapache:4.15from

ustcweizhou:4.15-check-systemvm-template-before-db

Feb 24, 2021

Commits on Jan 12, 2021

Upgrade: check systemvm template before db changes
ustcweizhou
committed

Commits on Jan 19, 2021

Upgrade: move some codes to a separated method
ustcweizhou
committed

Commits on Feb 2, 2021

#4582 add txn.commit()
ustcweizhou
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