openvz/8: add OpenVZ command line man pages

These are .8 man pages from the following OpenVZ packages:
* vzctl 4.5
* ploop 1.9
* vzquota 3.1
* vzstats 0.5.1

Those packages are available from git.openvz.org.

Note that .5 man pages are not added.

Signed-off-by: Kir Kolyshkin <kir@openvz.org>