LKE-3931: Set maxVolumesPerNode to 7

[rsienko]

This is a quick fix for the default case when we have 8 slots and one slot is already taken by boot disk. There may be more slots in use by non-PVC volumes such as swap but they are not the default in LKE.

fixes #154

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[luthermonson]

@kitknox i think you should weigh in on this, there is some logic he suggested we could use to check the disks on the node and make this limit more dynamic. this is probably the quick fix though and we could go with this and ticket the better fix if its too much of a time sink today

[kitknox]

In the current situation where the API attempts to enforce a limit of 8 block devices, this is an improvement. The downside is that work is planned to improve that to align with the host enforced scalable limit at which point this will be worse. Given workloads are already impacted by the current oversubscription issue there is value in getting this out there but we need to ensure we come back to this quickly when the upstream API shifts.