pci-passthrough-whitelist accepts config with newlines which generates errors in nova.conf

[Adam Dyess]

cs:nova-compute-322

applications:
  nova-compute-kvm-sriov:
      options:
        pci-passthrough-whitelist: |
         [
          {"devname":"eth0", "physical_network":"physnet1"},
          {"devname":"eth1", "physical_network":"physnet1"}
         ]

This yaml when applied to the pci_passthrough-whitelist results in newlines in nova.conf which cannot be parsed by nova-compute. The charm should be able at the minimum

sanitized = json.loads(...) the config item
and then
context['pci_passthrough_whitelist'] = json.dumps(sanitized)