sql: goroutine spawned for vtable generators does not go through stopper

[knz]

The code in sql/virtual_table.go contains the following:

  wg.Add(1)
  go func() {
    defer wg.Done()
  ...

it should use the stopper and run an Async task instead

or alternatively share the goroutine registration stuff with the stopper to get the cancellation behavior upon server stop.

at the very least it needs a call to logcrash.RecoverOnPanic...

[knz]

cc @yuzefovich @rafiss for triage