[ci] Switch lint to use cloud pool

Lint doesn't need access to tools available only on the local runner, we
can use Azure cloud resources for that to reduce the load on our
runners.
diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index 18f24f4..c6e1dd1 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -23,7 +23,8 @@
   jobs:
   - job: "lint"
     displayName: "Run code quality checks (lint)"
-    pool: "Default"
+    pool:
+      vmImage: "ubuntu-16.04"
     steps:
     - bash: |
         sudo apt-get install -y python3 python3-pip build-essential srecord python3-setuptools zlib1g-dev libusb-1.0 clang-format