criu: print criu and kernel versions from log_init()

log_init() opens a log file. We want to have criu and kernel versions in
each log file, so it looks reasonable to print them from log_init().

Without this patch, versions are not printed, if criu is called in the
swrk mode.

Reviewed-by: Dmitry Safonov <0x7f454c46@gmail.com>
Acked-by: Adrian Reber <areber@redhat.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>