feat(firecracker): run the post-build agent-image smoke test too

Closes the gap left in #354: docker and macos-container already
smoke-test a freshly built agent image before launch; firecracker
built the image via its own docker_mod-based path but never ran the
check. Same one-liner as the other two backends now that _build_agent_image
uses docker_mod.build_image.

bot_bottle/backend/firecracker/launch.py

@@ -24,6 +24,7 @@ from contextlib import ExitStack, contextmanager
 from pathlib import Path
 from typing import Callable, Generator
 
+from ...agent_provider import runtime_for
 from ...bottle_state import (
     egress_state_dir,
     git_gate_state_dir,
@@ -180,6 +181,9 @@ def _build_agent_image(plan: FirecrackerBottlePlan) -> FirecrackerBottlePlan:
             agent_provision=dataclasses.replace(plan.agent_provision, image=committed),
         )
     docker_mod.build_image(plan.image, _REPO_DIR, dockerfile=plan.dockerfile_path)
+    docker_mod.verify_agent_image(
+        plan.image, runtime_for(plan.agent_provider_template).smoke_test,
+    )
     return plan