Consistently use ubuntu-18.04

We currently use a mix of 16.04 and 18.04.

Change-Id: I62e64a7cadd2bea08ee35933757d094af9468d03
Signed-off-by: Matthew Sykes <sykesmat@us.ibm.com>

ci/azure-pipelines-merge.yml

@@ -16,7 +16,7 @@ variables:
 jobs:
   - job: UnitTests
     pool:
-      vmImage: ubuntu-16.04
+      vmImage: ubuntu-18.04
     steps:
       - template: install_deps.yml
       - checkout: self

ci/azure-pipelines-release.yml

@@ -20,7 +20,7 @@ stages:
     jobs:
       - job: Build
         pool:
-          vmImage: ubuntu-16.04
+          vmImage: ubuntu-18.04
         container: golang:$(GOVER)
         strategy:
           matrix:
@@ -46,7 +46,7 @@ stages:
     jobs:
       - job: Docker
         pool:
-          vmImage: ubuntu-16.04
+          vmImage: ubuntu-18.04
         steps:
           - template: install_deps.yml
           - checkout: self
@@ -66,7 +66,7 @@ stages:
     jobs:
       - job: Release
         pool:
-          vmImage: ubuntu-16.04
+          vmImage: ubuntu-18.04
         steps:
           - download: current
             patterns: '*.tar.gz'

vagrant/Vagrantfile

@@ -7,7 +7,7 @@
 
 Vagrant.require_version ">= 1.7.4"
 Vagrant.configure('2') do |config|
-  config.vm.box = "bento/ubuntu-16.04"
+  config.vm.box = "bento/ubuntu-18.04"
   config.vm.synced_folder "..", "/home/vagrant/go/src/github.com/hyperledger/fabric"
   config.ssh.forward_agent = true