Add pigz support to vzctl create

It can speedup unpack template about 2 and more times.
As example runnig vzctl create with custom 702M size template:
(second and third run vzctl create with this template, file cache already warmed)
 - without pigz
    702MB 0:00:14 [49.4MB/s]

 - with pigz
    702MB 0:00:07 [90.9MB/s]
1 file changed