[antlir2][migration] fix passthrough of test hostname

Summary: Title

Test Plan:
```
❯ buck2 test 'fbcode//mode/opt-tsan' fbcode//schedulers/tangram/agent/tests/sudo:container_service_vm_tests.nspawn -- --exact 'schedulers/tangram/agent/tests/sudo:container_service_vm_tests.nspawn - ContainerServiceVmTests.testSystemdListings'
Buck UI: https://www.internalfb.com/buck2/f9ecb3f5-5a19-4ef2-9183-286d0c6e95c1
Test UI: https://www.internalfb.com/intern/testinfra/testrun/13229323919810798
Note:    Using experimental modern dice
Network: Up: 1.4MiB  Down: 0B  (reSessionID-20ed7859-d589-4416-aa86-ede7397efae2)
Jobs completed: 40. Time elapsed: 14.9s.
Cache hits: 0%. Commands: 8 (cached: 0, remote: 0, local: 8)
Tests finished: Pass 1. Fail 0. Fatal 0. Skip 0. Build failure 0
```

Reviewed By: justintrudell

Differential Revision: D52165962

fbshipit-source-id: 5c87ace9bf3ed71b7c1111a309fdb2a97203a293

antlir/bzl/image_cpp_unittest.bzl

@@ -30,6 +30,7 @@ def image_cpp_unittest(
         boot = boot,
         run_as_user = run_as_user,
         boot_requires_units = ["dbus.socket"] if (boot and container_opts and container_opts.boot_await_dbus) else [],
+        hostname = hostname,
         fake_buck1 = struct(
             fn = antlir2_shim.fake_buck1_test,
             name = name,

antlir/bzl/image_python_unittest.bzl

@@ -43,6 +43,7 @@ def image_python_unittest(
         boot = boot,
         run_as_user = run_as_user,
         boot_requires_units = ["dbus.socket"] if (boot and container_opts and container_opts.boot_await_dbus) else [],
+        hostname = hostname,
         fake_buck1 = struct(
             fn = antlir2_shim.fake_buck1_test,
             name = name,

antlir/bzl/image_rust_unittest.bzl

@@ -29,6 +29,7 @@ def image_rust_unittest(
         run_as_user = run_as_user,
         boot_requires_units = ["dbus.socket"] if (boot and container_opts and container_opts.boot_await_dbus) else [],
         crate = rust_unittest_kwargs.pop("crate", name + "_unittest"),
+        hostname = hostname,
         fake_buck1 = struct(
             fn = antlir2_shim.fake_buck1_test,
             name = name,