Fix loop in redis-reconfigure.sh

Fix loop to poll redis nodes.

The following xargs command was failing due to its input being a space-delimited string rather than newline-delimited.

echo $hosts | xargs -n1 -I{} ssh "{}.c.${gitlab_project}.internal" ...

Assigning the output of seq to the $hosts variable implicitly flattens its newlines into spaces.

So xargs passed the whole space-delimited string at once to ssh as the target hostname, which of course is invalid.

Resulting error:

kex_exchange_identification: Connection closed by remote host
xargs: ssh: exited with status 255; aborting

This issue may have been an incompatibility between xargs behavior on a Mac versus Linux, but at least when run on Linux (specifically tested with Ubuntu's xargs 4.7.0 from the findutils package), by default it expects input to be newline delimited, not space-delimited:

msmiley@neri:~$ xargs --version | head -n1
xargs (GNU findutils) 4.7.0

msmiley@neri:~$ echo 1 2 3 | xargs -I{} -n1 echo "Val: {}"
Val: 1 2 3

msmiley@neri:~$ seq 3 | xargs -I{} -n1 echo "Val: {}"
Val: 1
Val: 2
Val: 3

In this MR, I replaced xargs with a for loop.

That is sufficient to avoid the bug, since for splits words on either spaces or newlines.

Also, since the $hosts variable was not used elsewhere, I went ahead and got rid of it, moving its subcommand directly to the for loop.