`ivy scenarios` initialize grpc stubs with default shard/realm

Yahcli's `ivy` command doesn't designate the spec's target network prior to initializing its grpc stubs. The net effect is that `HapiSpec`'s non-trivial initialization sequence executes with differing consequences when done via gradle's `testSubprocess` command vs. running a command directly from the yahcli jar. In the `testSubprocess` case gradle gets around this behavior by explicitly setting the shard/realm via system properties prior to launching `HapiSpec`'s startup sequence. Running the yahcli jar, however, has no such bootstrap, and its commands fail to find any matching stubs.