cmd: Make changefeed sort dir visible (#2222)

[ti-chi-bot]

This is an automated cherry-pick of #2222

What problem does this PR solve?

This PR try to revert part of the work in #1784, also fix a problem when try to set data-dir by existed changefeed information.

• sort-dir can be read but cannot be written.
• create dir temporarily when try to find best data-dir by existed changefeed information.

What is changed and how it works?

revert changefeed info struct and related read and write.

Check List

Tests

• Unit test

Code changes

Side effects

Related changes

Release note

• No release note

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has not been approved.

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[ti-chi-bot]

@ti-chi-bot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick, it must first be approved by the collaborators.

AFTER it has been approved by collaborators, please ping the release team in a comment to request a cherry pick review.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[3AceShowHand]

this will be done in #2069