debian/cephadm.postinst: specify --home when adduser

quote from adduser/NEWS.Debian.gz:

>  System user home defaults to /nonexistent if --home is not specified.
>  Packages that call adduser to create system accounts should explicitly
>  specify a location for /home (see Lintian check
>  maintainer-script-lacks-home-in-adduser).

so let's follow this change in adduser. otherwise "cephadm"
would have a $HOME at `/nonexistent`.

Fixes: https://tracker.ceph.com/issues/64069
Signed-off-by: Kefu Chai <[email protected]>

Author: tchaikov

debian/cephadm.postinst

@@ -28,6 +28,7 @@ case "$1" in
          adduser --quiet \
                  --system \
                  --disabled-password \
+                 --home /home/cephadm \
                  --gecos 'cephadm user for mgr/cephadm' \
                  --shell /bin/bash cephadm 2>/dev/null || true
          echo "..done"