Flush the shell console after each command

This patch fixes the file manager on android-n-preview-2 (and maybe
other roms/systems). Observed behavior: no output is produced at StdIn
or StdErr after writing commands to the shell console. This leads to a
timeout and a reallocation of the console in an endless loop. Flushing
the output stream fixes the problem. Not sure if there was a good reason
for not doing it in general.

Change-Id: Ia87aa5065f6c62f133de4bbde4b4a32a4388d784