metropolis: unify utility packages

One last sweeping rename / reshuffle.

We get rid of //metropolis/node/common and //golibs, unifying them into
a single //metropolis/pkg meta-package.

This is to be documented somwhere properly, but here's the new logic
behind selecting where to place a new library package:

 - if it's specific to k8s-on-metropolis, put it in
   //metropolis/node/kubernetes/*. This is a self-contained tree that
   other paths cannot import from.
 - if it's a big new subsystem of the metropolis core, put it in
   //metropolis/node/core. This can be imported by anything in
   //m/n (eg the Kubernetes code at //m/n/kubernetes
 - otherwise, treat it as generic library that's part of the metropolis
   project, and put it in //metropolis/pkg. This can be imported by
   anything within //metropolis.

This will be followed up by a diff that updates visibility rules.

Test Plan: Pure refactor, CI only.

X-Origin-Diff: phab/D683
GitOrigin-RevId: 883e7f09a7d22d64e966d07bbe839454ed081c79
diff --git a/metropolis/test/nanoswitch/BUILD b/metropolis/test/nanoswitch/BUILD
index ee8c2c2..fa7e271 100644
--- a/metropolis/test/nanoswitch/BUILD
+++ b/metropolis/test/nanoswitch/BUILD
@@ -8,10 +8,10 @@
     visibility = ["//visibility:private"],
     deps = [
         "//metropolis/node:go_default_library",
-        "//metropolis/node/common/supervisor:go_default_library",
-        "//metropolis/node/core/logtree:go_default_library",
         "//metropolis/node/core/network/dhcp4c:go_default_library",
         "//metropolis/node/core/network/dhcp4c/callback:go_default_library",
+        "//metropolis/pkg/logtree:go_default_library",
+        "//metropolis/pkg/supervisor:go_default_library",
         "//metropolis/test/launch:go_default_library",
         "@com_github_google_nftables//:go_default_library",
         "@com_github_google_nftables//expr:go_default_library",
diff --git a/metropolis/test/nanoswitch/nanoswitch.go b/metropolis/test/nanoswitch/nanoswitch.go
index 2569ab6..91d270b 100644
--- a/metropolis/test/nanoswitch/nanoswitch.go
+++ b/metropolis/test/nanoswitch/nanoswitch.go
@@ -39,10 +39,10 @@
 	"golang.org/x/sys/unix"
 
 	common "git.monogon.dev/source/nexantic.git/metropolis/node"
-	"git.monogon.dev/source/nexantic.git/metropolis/node/common/supervisor"
-	"git.monogon.dev/source/nexantic.git/metropolis/node/core/logtree"
 	"git.monogon.dev/source/nexantic.git/metropolis/node/core/network/dhcp4c"
 	dhcpcb "git.monogon.dev/source/nexantic.git/metropolis/node/core/network/dhcp4c/callback"
+	"git.monogon.dev/source/nexantic.git/metropolis/pkg/logtree"
+	"git.monogon.dev/source/nexantic.git/metropolis/pkg/supervisor"
 	"git.monogon.dev/source/nexantic.git/metropolis/test/launch"
 )