CopySchemaShard with a passing integration test

primary: @alainjobart 
FYI: @enisoc 

This adds CopySchemaShard to vtctl, as discussed (using raw ExecuteFetch instead of ApplySchema, and only writing on masters with replication on). I added some unit tests and one full integration test - not planning on doing a mocked test.

I do still need to modify vtworker to depend fully on wrangler for creating schemas instead of copying them itself, and fixing up tests so that all passes.

@alainjobart, I'd especially appreciate a careful look at if locking is appropriate/necessary, and make sure that I'm not stepping on your toes with contexts.
This should be moved up and out of the range createSql loop. Only needs to be done once, and you can pass in the tablet *topo.TabletInfo in here, not the alias.