Rebase #3450 Use destination master for comparison during split clone

[deepthi]

After rebase, made the following changes:

1. set attempt := 1 in nextWithRetries
2. change worker test to stop master while the copy is running instead of before starting SplitClone
3. Fix bug in cancelVerticalResharding that was causing vertical_split tests to fail with this change

@tirsen Please review

[sougou]

@rafael @tirsen: @deepthi has fixed up this old PR.
Can you eyeball this before I merge?

[tirsen]

@mpawliszyn Can you have a look too. I think you've been working on the retries here as well right?

[tirsen]

I'm guessing you've only changed test code not production code? In that case LGTM, otherwise could you point to any production code you changed?

[deepthi]

@tirsen
here are the changes from your PR:

1. restartable_result_reader.go:nextWithRetries
   attempt := 1. You had changed this to attempt := 0
2. executor.go:checkError
   - case errNo == "2002" || errNo == "2006" || errNo == "2013":
+ case errNo == "2002" || errNo == "2006" || errNo == "2013" || errNo == "1053":
   This is to handle a destination master mysql going down and coming back up while SplitClone is running