Fixes #282 use requiredby to make a hard dependency chain

[Klaas-]

Fixes #282 use requiredby to make a hard dependency chain

[rh-atomic-bot]

Can one of the admins verify this patch?
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[rhatdan]

@rhvgoyal PTAL
As I recall we wanted to allow this to fail in order to allow Docker running with Devicemapper on loopback devices to work. I think containers-storage-setup would fail in that situation and cause Docker to use loopback devices. Now that we default to using Overlay, we could perhaps make the switch.

[Klaas-]

So there is a situation where you expect the service to fail? Wouldn't it be better/easier to just not use the service ie when dm on loopback "systemctl disable docker-storage-setup"? or even fully remove the package and only install it when needed?