criu: don't show long usage in case of error
criu: don't show long usage in case of error

* Don't show long usage in case of usage error, otherwise an actual
  error message will be lost in long output.

* Print error if command is not specified.

* Return 0 if criu --help is used.

Signed-off-by: Kir Kolyshkin <c0159612b0ef32139322233232df1a0d189c4b9b@openvz.org>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@parallels.com>

gonkulator/criu,AuthenticEshkinKot/criu,gablg1/criu,efiop/criu,ldu4/criu,fbocharov/criu,rentzsch/criu,ldu4/criu,kawamuray/criu,tych0/criu,fbocharov/criu,wtf42/criu,biddyweb/criu,LK4D4/criu,fbocharov/criu,AuthenticEshkinKot/criu,rentzsch/criu,eabatalov/criu,sdgdsffdsfff/criu,LK4D4/criu,eabatalov/criu,sdgdsffdsfff/criu,sdgdsffdsfff/criu,ldu4/criu,svloyso/criu,marcosnils/criu,AuthenticEshkinKot/criu,biddyweb/criu,kawamuray/criu,LK4D4/criu,gonkulator/criu,wtf42/criu,gablg1/criu,sdgdsffdsfff/criu,KKoukiou/criu-remote,svloyso/criu,fbocharov/criu,gonkulator/criu,gablg1/criu,efiop/criu,LK4D4/criu,fbocharov/criu,eabatalov/criu,gablg1/criu,tych0/criu,kawamuray/criu,marcosnils/criu,gonkulator/criu,AuthenticEshkinKot/criu,eabatalov/criu,rentzsch/criu,svloyso/criu,efiop/criu,biddyweb/criu,marcosnils/criu,sdgdsffdsfff/criu,rentzsch/criu,efiop/criu,wtf42/criu,svloyso/criu,ldu4/criu,LK4D4/criu,rentzsch/criu,marcosnils/criu,efiop/criu,KKoukiou/criu-remote,efiop/criu,tych0/criu,gonkulator/criu,AuthenticEshkinKot/criu,KKoukiou/criu-remote,eabatalov/criu,ldu4/criu,kawamuray/criu,AuthenticEshkinKot/criu,KKoukiou/criu-remote,gablg1/criu,tych0/criu,marcosnils/criu,LK4D4/criu,KKoukiou/criu-remote,tych0/criu,biddyweb/criu,wtf42/criu,fbocharov/criu,kawamuray/criu,gonkulator/criu,sdgdsffdsfff/criu,wtf42/criu,gablg1/criu,rentzsch/criu,kawamuray/criu,eabatalov/criu,wtf42/criu,biddyweb/criu,biddyweb/criu,marcosnils/criu,ldu4/criu,svloyso/criu,KKoukiou/criu-remote,tych0/criu,svloyso/criu