fix #2834: skip refs in config_with_pending_array

With the refactoring of config_with_pending_array in
daf8fca57a a few sanity checks on parsed configs
were dropped.

One case where a config value should be skipped, instead of parsed and added
is when the value is not scalar. This is the case for the raw lxc keys
(e.g. lxc.init.cmd, lxc.apparmor.profile) - which get added as array to the
'lxc' key.

This patch reintroduces the skipping of non-scalar values, when parsing the
config but not for the pending values.
From a short look through the commit history the sanity checks were in place
since 2014 (introduced in qemu-server for handling pending configuration
changes), and their removal did not cause any other regressions.
To my knowledge only the raw lxc config keys are parsed into a non-scalar
value.

Tested by adding a 'lxc.init.cmd' key to a container config.

Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>

PVE/GuestHelpers.pm

@@ -214,6 +214,8 @@ sub config_with_pending_array {
 
     my $res = [];
     foreach my $opt (keys %$conf) {
+	next if ref($conf->{$opt});
+
 	my $item = {
 	    key => $opt,
 	    value => $conf->{$opt},