Previously, the exec example would fail if it could not write the whole
read buffer to stdout. With this changes, the exec example will be able
to write parts of the buffer until the whole buffer is written.
This makes the exec example to run when the stdout buffer is small.
Signed-off-by: Anderson Toshiyuki Sasaki <ansasaki@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
