CI linux agent changes (digital-asset#509)

* ci: always use the linux-pool

reduce the difference of environment between external and internal
contributions

* infra: tweak the linux cache warmup script

Don't share the same bazel cache directory with the disk cache, which is
something else. Be more specific about the target. Clean after yourself.

* infra: bump the linux agent disk to 200GB

avoid running out of disk space

azure-pipelines.yml

@@ -20,10 +20,8 @@ jobs:
   - job: linux
     timeoutInMinutes: 360
     pool:
-      ${{ if eq(variables['System.PullRequest.IsFork'], 'true') }}:
-        vmImage: 'ubuntu-16.04'
-      ${{ if eq(variables['System.PullRequest.IsFork'], 'false') }}:
-        name: 'linux-pool'
+      # vmImage: 'ubuntu-16.04'
+      name: 'linux-pool'
     steps:
       - template: ci/build-unix.yml
         parameters:

infra/vsts_agent_linux.tf

@@ -39,7 +39,7 @@ resource "google_compute_instance_template" "vsts-agent-linux" {
   labels       = "${local.labels}"
 
   disk {
-    disk_size_gb = 100
+    disk_size_gb = 200
     disk_type    = "pd-ssd"
     source_image = "ubuntu-os-cloud/ubuntu-1604-lts"
   }

infra/vsts_agent_linux_startup.sh

@@ -106,11 +106,18 @@ systemctl restart nix-daemon
 # around, even when their caches are only warmed up halfway
 su --login vsts <<'CACHE_WARMUP'
 # user-wide bazel disk cache override
-echo "build --disk_cache=~/.cache/bazel" > ~/.bazelrc && \
-git clone https://github.com/digital-asset/daml && \
-cd daml && \
-./ci/dev-env-install.sh && \
-./build.sh "_$(uname)" || true
+echo "build:linux --disk_cache=~/.bazel-cache" > ~/.bazelrc
+
+# clone and build
+(
+  git clone https://github.com/digital-asset/daml
+  cd daml
+  ./ci/dev-env-install.sh
+  ./build.sh "_$(uname)"
+) || true
+
+# free some disk space
+rm -rf ~/daml
 CACHE_WARMUP
 
 # Purge old agents