ASM-2867 optional installer_options in task scripts

Handle the case where node.policy.node_metadata is nil in razor
task scripts. It is not currently being passed for VMs. Although
it probably should be passed in that case it would be good for
the razor task scripts to work without it.
Merge pull request #53 from gavin-scott/optional-installer-options

ASM-2867 optional installer_options in task scripts