m/c/metroctl: exercise the takeownership command

This introduces a new test harness together with a test exercising
takeownership.

Change-Id: I998506093c25e489d8cb2810e90b4c94530bf4a6
Reviewed-on: https://review.monogon.dev/c/monogon/+/839
Tested-by: Jenkins CI
Reviewed-by: Sergiusz Bazanski <serge@monogon.tech>
diff --git a/metropolis/node/BUILD.bazel b/metropolis/node/BUILD.bazel
index a193c31..0904ec1 100644
--- a/metropolis/node/BUILD.bazel
+++ b/metropolis/node/BUILD.bazel
@@ -147,6 +147,7 @@
         "//metropolis/node/build/mkimage",
     ],
     visibility = [
+        "//metropolis/cli/metroctl/test:__subpackages__",
         "//metropolis/test/e2e:__subpackages__",
         "//metropolis/test/launch:__subpackages__",
     ],
@@ -214,6 +215,7 @@
     cp tpm/ca/signkey.pem $(location tpm/signkey.pem)
     """,
     visibility = [
+        "//metropolis/cli/metroctl/test:__subpackages__",
         "//metropolis/test/e2e:__subpackages__",
         "//metropolis/test/launch:__subpackages__",
     ],