Program to remove a previous SPDK Installation.

[pykello]

After we call Prog::Storage::RemoveSpdk(spdk_installation), it should:

• Error out if this is the only Spdk installation with positive allocation_weight on the host.
• Set spdk_installation.allocation_weight to 0 so we don't allocate Vms to that Spdk anymore.
• Maybe weight for 30 seconds to avoid concurrency issues in the next step. That is, a Vm::Nexus might have seen the previous allocation_weight, but hasn't created the volumes yet.
• Wait until all VmStorageVolumes with that Spdk have been removed.
• Disable & stop the Spdk service in the host.
• Remove all the services & paths specific to that Spdk installation. See rhizome/host/lib/spdk_setup.rb.
• Remove the database records.