Set aside tests on ubuntu 16.04 for now

spread.yaml

@@ -16,9 +16,9 @@ backends:
     location: snapd-spread/us-east1-b
     halt-timeout: 2h
     systems:
-      - ubuntu-16.04-64:
-            workers: 1
-            storage: 12G
+      # - ubuntu-16.04-64:
+      #       workers: 1
+      #       storage: 12G
       - ubuntu-18.04-64:
             storage: 12G
             workers: 1
@@ -37,9 +37,9 @@ backends:
   qemu:
     memory: 4G
     systems:
-      - ubuntu-16.04-64:
-            username: ubuntu
-            password: ubuntu
+      # - ubuntu-16.04-64:
+      #       username: ubuntu
+      #       password: ubuntu
       - ubuntu-18.04-64:
             username: ubuntu
             password: ubuntu
@@ -99,7 +99,7 @@ prepare: |
   apt install -y snapd libc6-dev gcc-multilib git
   snap install core20 --channel=latest/edge
   snap install --classic snapcraft
-  snap install --classic yq
+  snap install yq
   snap install --classic go --channel=1.19/stable
   unset SHELL
   git clone https://git.launchpad.net/ubuntu-images