zdtm.py: bind-mount a test root as slave
zdtm.py: bind-mount a test root as slave

In this case it has an external master_id and we want to test that
criu can handle it correctly.

Signed-off-by: Andrew Vagin <74c05afa918858348d6db8037d82fa8124870113@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@parallels.com>

KKoukiou/criu-remote,AuthenticEshkinKot/criu,AuthenticEshkinKot/criu,fbocharov/criu,wtf42/criu,KKoukiou/criu-remote,wtf42/criu,eabatalov/criu,fbocharov/criu,fbocharov/criu,fbocharov/criu,ldu4/criu,eabatalov/criu,svloyso/criu,ldu4/criu,fbocharov/criu,tych0/criu,efiop/criu,eabatalov/criu,fbocharov/criu,tych0/criu,wtf42/criu,svloyso/criu,ldu4/criu,wtf42/criu,svloyso/criu,KKoukiou/criu-remote,eabatalov/criu,efiop/criu,efiop/criu,wtf42/criu,tych0/criu,wtf42/criu,KKoukiou/criu-remote,tych0/criu,eabatalov/criu,tych0/criu,efiop/criu,efiop/criu,svloyso/criu,KKoukiou/criu-remote,tych0/criu,svloyso/criu,KKoukiou/criu-remote,AuthenticEshkinKot/criu,ldu4/criu,svloyso/criu,AuthenticEshkinKot/criu,AuthenticEshkinKot/criu,ldu4/criu,AuthenticEshkinKot/criu,eabatalov/criu,ldu4/criu,efiop/criu