Define Sandbox `clients` when running `versioning hot code push test`.
Define Sandbox `clients` when running `versioning hot code push test`.

Since this test utilizes the `testWithAllClients` technique, which runs
the tests in various clients/browsers, it's necessary for the tests
`Sandbox` to define `clients`, otherwise the function within
`testWithAllClients` will not be executed at all.  This was causing this
particular test to always return success (it was running without failure
on exactly zero clients).

Also the technique of setting `this.baseTimeout` appeared to cause
problems, likely because it overrides various other values instead of
using `waitSecs` (we don't use the `baseTimeout` technique in other
places within self-tests either).

Discovered during testing, as mentioned in
https://github.com/meteor/meteor/pull/9439#pullrequestreview-83139232.

Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor