Fix overlay2 busy error on mount
Fix overlay2 busy error on mount

When mounting overlays which have children, enforce that
the mount is always performed as read only. Newer versions
of the kernel return a device busy error when a lower directory
is in use as an upper directory in another overlay mount.

Adds committed file to indicate when an overlay is being used
as a parent, ensuring it will no longer be mounted with an
upper directory.

Signed-off-by: Derek McGowan <e1c79a582b6629e6b39e9679f4bb964d25db4aa8@mcgstyle.net>

vdemeester/docker,jvanz/docker,konstruktoid/docker-1,SvenDowideit/docker,konstruktoid/docker-1,nalind/docker,cpuguy83/docker,Ramzec/docker,mahak/docker,moby/moby,yosifkit/docker,SvenDowideit/docker,paralin/docker,jimjag/docker,Mokolea/docker,thaJeztah/docker,moby/moby,paralin/docker,yongtang/docker,thaJeztah/docker,gnailuy/docker,nawawi/docker,paralin/docker,mahak/docker,moul/docker,ibuildthecloud/docker,thaJeztah/docker,gnailuy/docker,jimjag/docker,gnailuy/docker,dims/docker,Mokolea/docker,estesp/docker,kojiromike/docker,ibuildthecloud/docker,djs55/docker,kojiromike/docker,justincormack/docker,cpuguy83/docker,Ramzec/docker,vdemeester/docker,pradipd/moby,bearstech/moby,trebonian/docker,nawawi/docker,AkihiroSuda/docker,flavio/docker,estesp/docker,pradipd/moby,konstruktoid/docker-upstream,mahak/docker,trebonian/docker,bearstech/moby,SvenDowideit/docker,dims/docker,Ramzec/docker,jvanz/docker,docker/docker,Ramzec/docker,trebonian/docker,bearstech/moby,moul/docker,gnailuy/docker,mahak/docker,moby/moby,bearstech/moby,justincormack/docker,konstruktoid/docker-1,jvanz/docker,dims/docker,jimjag/docker,djs55/docker,cpuguy83/docker,jimjag/docker,moby/moby,nalind/docker,docker/docker,docker/docker,cpuguy83/docker,nalind/docker,ibuildthecloud/docker,konstruktoid/docker-upstream,nalind/docker,jthelin/docker,yongtang/docker,justincormack/docker,nawawi/docker,ibuildthecloud/docker,jthelin/docker,konstruktoid/docker-upstream,Mokolea/docker,yosifkit/docker,thaJeztah/docker,yongtang/docker,AkihiroSuda/docker,flavio/docker,djs55/docker,paralin/docker,moul/docker,flavio/docker,ibuildthecloud/docker,yosifkit/docker,jameszhan/docker,AkihiroSuda/docker,yosifkit/docker,kojiromike/docker,flavio/docker,pradipd/moby,trebonian/docker,vdemeester/docker,nawawi/docker,moul/docker,AkihiroSuda/docker,estesp/docker,konstruktoid/docker-upstream,jameszhan/docker,Mokolea/docker,jameszhan/docker