vzctl create: improve "no ploop" error message

As pointed out in bug #2993, the message about absent ploop library
is not clear enough. Expland it, telling how to revert to simfs in case
a user don't want to or can't use ploop.

https://bugzilla.openvz.org/show_bug.cgi?id=2993

Reported-by: Ionut Biru <biru.ionut@gmail.com>
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
1 file changed