allow native safari automation on real devices >= 7

turns out maybe it was only 6.x that didn't allow us to do this - fix #3331

also, create a mode where if we expect instruments to exit, we don't try to
connect the bootstrap to the command proxy, avoiding error crashes
- fix #3539, fix #3397 

this depends on https://github.com/appium/appium-uiauto/pull/49