cmd,task: disable stray command line args, and log the command in LogArguments (#579)

[ti-srebot]

cherry-pick #579 to release-4.0

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What problem does this PR solve?

1. It was confusing that --checksum false does not actually disable checksum, because --checksum as a boolean flag already means --checksum=true. So --checksum false becomes --checksum=true false, and that extra false becomes a stray argument, which is ignored before this PR.

2. LogArguments did not record whether it is a "backup" or "restore" making it a bit hard to determine the data direction when reading logs.

What is changed and how it works?

1. Added Args: cobra.NoArgs to all leaf commands so using --checksum false will result in

   Error: unknown command "false" for "br backup full"
   

   rather than silently keeping checksum.

2. Record the command being executed inside LogArguments.

   Note that I changed LogArguments from using VisitAll to Visit. Originally in add log for cmd arguments and duration for checksum #55 it was using VisitAll to print all args, however it was changed in Don't log secret of s3. #292 to condition on f.Changed, so perhaps let's just use Visit directly 🙃.

Check List

Tests

• Manual test (add detailed scripts or steps below)
  • Run and check the log.

Code changes

Side effects

Related changes

• Need to cherry-pick to the release branch

Release Note

• BR no longer accepts --checksum false in command line, which did not disable checksum. The correct usage always include the = sign: --checksum=false.

[kennytm]

/rebuild

[3pointer]

lgtm

[glorv]

LGTM

[glorv]

/merge

[ti-srebot]

/run-all-tests