RecoverySystemService: Dump exception stack on IOExceptions.

We occasionally hit "java.io.IOException: Connection reset by peer" when
communicating with uncrypt. Change to print verbose exception stack for
future debugging.

Also conservatively change the two potential causes: a) by removing the
call to dos.flush() after sending the last status code; b) by closing
the streams quietly instead.

Bug: 27782920
Change-Id: Ice6da1f27cb1ee83207c9f34958c0e012270167e