[TestEnv] Add fast start mode
Created by: derkling
When we run a set of tests, the really first connection is usually required just to reboot the board to start with a new kernel. In this case the really first connection can avoid to initialize all the modules to be as fast as possible.
It can be useful to add a "fast mode" connection flag to the TestEnv module which grants only to have a valid SSH/ADB connection to the target without any other platform specific initializations.