feat(exchain): testnet.sh add restart opt

[zibuyu28]

• Targeted PR against correct branch (see CONTRIBUTING.md)

• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.

• Wrote tests

• Updated relevant documentation (docs/)

• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md

• Reviewed Files changed in the github PR explorer

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For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
• Squashed all commits, uses message "Merge PR #XYZ: [title]" (coding standards)

[codecov-commenter]

Codecov Report

Merging #3195 (cadd0ba) into dev (39c86b1) will not change coverage.
The diff coverage is n/a.

❗ Current head cadd0ba differs from pull request most recent head 7ec4a81. Consider uploading reports for the commit 7ec4a81 to get more accurate results

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@@           Coverage Diff           @@
##              dev    #3195   +/-   ##
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  Coverage   36.46%   36.46%           
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  Files         444      444           
  Lines       46606    46606           
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  Hits        16993    16993           
  Misses      28347    28347           
  Partials     1266     1266