Create a Snapshot of a vApp with vCenter and PowerCLI

To my surprise the ability to snapshot an entire vApp is only available in vCloud Director, the feature is not in vCenter (as of 5.5). While not a perfect solution, a similar result can be achieved using PowerCLI. Initially I suspected the RunAsync parameter would need to be specified in the script, but that turned out not to be the case as the snapshots get created in parallel without it.