luci2-io-helper: bugfix buckup script read timeout
Reading files from stdin will block for ever. The uhttpd is killing the
backup process after script_timeout.
Switching read to non blocking mode and add a waitpid for the slave
process does not end in a script_timeout anymore.
Signed-off-by: Florian Eckert <Eckert.Florian@googlemail.com>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>