Fix bash remediation for sysctl template

The remediation breaks systemd-sysctl when executed multiple times.

On first run, settings are correctly added to /etc/sysctl.conf and
loaded by systemd-sysctl via the symlink
/etc/sysctl.d/99-sysctl.conf -> /etc/sysctl.conf.

On second run, the same settings are commented out in
/etc/systcl.d/99-sysctl.conf, replacing the symlink with a copy of the file.
Although the settings are again added to /etc/sysctl.conf, these
are not loaded by systemd-sysctl due to the broken link.

Fixes https://bugs.launchpad.net/usg/+bug/2056150

shared/templates/sysctl/bash.template

@@ -12,12 +12,16 @@ for f in /etc/sysctl.d/*.conf /run/sysctl.d/*.conf /usr/local/lib/sysctl.d/*.con
 {{% else %}}
 for f in /etc/sysctl.d/*.conf /run/sysctl.d/*.conf /usr/local/lib/sysctl.d/*.conf; do
 {{% endif %}}
+
+  # skip systemd-sysctl symlink (/etc/sysctl.d/99-sysctl.conf -> /etc/sysctl.conf)
+  if [[ "$(readlink -f "$f")" == "/etc/sysctl.conf" ]]; then continue; fi
+
   matching_list=$(grep -P '^(?!#).*[\s]*{{{ SYSCTLVAR }}}.*$' $f | uniq )
   if ! test -z "$matching_list"; then
     while IFS= read -r entry; do
       escaped_entry=$(sed -e 's|/|\\/|g' <<< "$entry")
       # comment out "{{{ SYSCTLVAR }}}" matches to preserve user data
-      sed -i "s/^${escaped_entry}$/# &/g" $f
+      sed -i --follow-symlinks "s/^${escaped_entry}$/# &/g" $f
     done <<< "$matching_list"
   fi
 done