spawn-1007006: Call host.exec from converters.convert too
spawn-1007006: Call host.exec from converters.convert too

This will allow the mozilla branch to use Task.spawn in converters as
well as commands.

Signed-off-by: Joe Walker <7a17872fbb32c7d760c9a16ee3076daead11efcf@mozilla.com>

mozilla/gcli,mozilla/gcli,mozilla/gcli,joewalker/gcli,joewalker/gcli