guix-install.sh: Fix incomplete installation.

‘false || return’ returns false, and
‘set -e’ aborts the script.  This leaves
Guix half installed with visual indication of error.

* etc/guix-install.sh (sys_customize_bashrc, sys_maybe_setup_selinux):
Explicitly return 0.

etc/guix-install.sh

@@ -581,7 +581,8 @@ sys_create_shell_completion()
 
 sys_customize_bashrc()
 {
-    prompt_yes_no "Customize users Bash shell prompt for Guix?" || return
+    prompt_yes_no "Customize users Bash shell prompt for Guix?" || return 0
+
     for bashrc in /home/*/.bashrc /root/.bashrc; do
         test -f "$bashrc" || continue
         grep -Fq '$GUIX_ENVIRONMENT' "$bashrc" && continue
@@ -615,7 +616,7 @@ sys_maybe_setup_selinux()
     done
 
     prompt_yes_no "Install SELinux policy that might be required to run guix-daemon?" \
-	|| return
+	|| return 0
 
     local var_guix=/var/guix/profiles/per-user/root/current-guix
     semodule -i "${var_guix}/share/selinux/guix-daemon.cil"