Add support to enter sideload mode directly

When the command file contains "--sideload" (as a result of 'adb reboot
sideload'), it goes into sideload mode directly. Text display will be
turned on by default. It waits for user interaction upon finishing.

When the command file contains "--sideload_auto_reboot", it enters
sideload mode silently. And it will reboot after the installation
regardless of its result, which is designed for automated testing purpose.

Change-Id: Ifdf173351221c7bbf635cfd32463b48e1fff5740