1. redis-cli can output --rdb data to stdout
but redis-cli also write some messages to stdout which will mess up the rdb.
2. Make redis-cli flush stdout when printing a reply
This was needed in order to fix a hung in redis-cli test that uses
--replica.
Note that printf does flush when there's a newline, but fwrite does not.
3. fix the redis-cli --replica test which used to pass previously
because it didn't really care what it read, and because redis-cli
used printf to print these other things to stdout.
4. improve redis-cli --replica test to run with both diskless and disk-based.
Co-authored-by: Oran Agra <oran@redislabs.com>
Co-authored-by: Viktor Söderqvist <viktor@zuiderkwast.se>
(cherry picked from commit 1eb4baa5b8e76adc337ae9fab49acc2585a0cdd0)
740c41c0f2