Backport PR
#2270: SSHLauncher tweaks
* use pipes.quote on SSH commands
* default SSHEngineSetLauncher to `ipengine` instead of import-based command.
This is actually the intended behavior, and only brings EngineSet inline with SSHEngine and SSHController, which both use the simplified command.
* Should be backported to 0.13.1
* Must be not be merged before
#2269
