Log update outputs in order

Although stdout and stderr are both redirected to log file with no
buffering, we are seeing some outputs are mixed in random order.
This is because ui_print commands from the updater are passed to the
recovery binary via a pipe, which may interleave with other outputs
that go to stderr directly.

In recovery, adding ui::PrintOnScreenOnly() function to handle
ui_print command, which skips printing to stdout. Meanwhile, updater
prints the contents to stderr in addition to piping them to recovery.

Change-Id: Idda93ea940d2e23a0276bb8ead4aa70a3cb97700