fix #1570: fix template backup with pigz

fix #1570: fix template backup with pigz

when using pigz the resulting commandline would look like:

pigz -p 4>file

which resulted in pigz erroring out because it got no parameter for -p
(because the shell interpreted the 4>file as a file descriptor)

this patch adds a space so that the resulting line is
pigz -p 4 > file

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
Reviewed-by: Thomas Lamprecht <t.lamprecht@proxmox.com>