ci: [refactor] Create setting for ephemeral config in .cirrus.yml

This allows easier switching between self-hosted runners and the
community cluster. Also, named variables can be documented better.

.cirrus.yml

@@ -3,11 +3,13 @@
 env:
   PACKAGE_MANAGER_INSTALL: "apt-get update && apt-get install -y"
   MAKEJOBS: "-j4"
-  DANGER_RUN_CI_ON_HOST: "1"  # Containers will be discarded after the run, so there is no risk that the ci scripts modify the system
   TEST_RUNNER_PORT_MIN: "14000"  # Must be larger than 12321, which is used for the http cache. See https://cirrus-ci.org/guide/writing-tasks/#http-cache
   CCACHE_SIZE: "200M"
   CCACHE_DIR: "/tmp/ccache_dir"
 
+cirrus_ephemeral_worker_template_env: &CIRRUS_EPHEMERAL_WORKER_TEMPLATE_ENV
+  DANGER_RUN_CI_ON_HOST: "1"  # Containers will be discarded after the run, so there is no risk that the ci scripts modify the system
+
 # https://cirrus-ci.org/guide/tips-and-tricks/#sharing-configuration-between-tasks
 base_template: &BASE_TEMPLATE
   skip: $CIRRUS_REPO_FULL_NAME == "bitcoin-core/gui" && $CIRRUS_PR == ""  # No need to run on the read-only mirror, unless it is a PR. https://cirrus-ci.org/guide/writing-tasks/#conditional-task-execution
@@ -69,6 +71,8 @@ task:
   << : *CREDITS_TEMPLATE
   lint_script:
     - ./ci/lint_run_all.sh
+  env:
+    << : *CIRRUS_EPHEMERAL_WORKER_TEMPLATE_ENV
 
 task:
   name: 'ARM [unit tests, no functional tests] [buster]'
@@ -76,6 +80,7 @@ task:
   container:
     image: debian:buster
   env:
+    << : *CIRRUS_EPHEMERAL_WORKER_TEMPLATE_ENV
     FILE_ENV: "./ci/test/00_setup_env_arm.sh"
 
 task:
@@ -84,6 +89,7 @@ task:
   container:
     image: ubuntu:focal
   env:
+    << : *CIRRUS_EPHEMERAL_WORKER_TEMPLATE_ENV
     FILE_ENV: "./ci/test/00_setup_env_win64.sh"
 
 task:
@@ -92,6 +98,7 @@ task:
   container:
     image: centos:8
   env:
+    << : *CIRRUS_EPHEMERAL_WORKER_TEMPLATE_ENV
     PACKAGE_MANAGER_INSTALL: "yum install -y"
     FILE_ENV: "./ci/test/00_setup_env_i686_centos.sh"
 
@@ -105,6 +112,7 @@ task:
   container:
     image: ubuntu:bionic
   env:
+    << : *CIRRUS_EPHEMERAL_WORKER_TEMPLATE_ENV
     FILE_ENV: "./ci/test/00_setup_env_native_qt5.sh"
 
 task:
@@ -115,6 +123,7 @@ task:
     cpu: 6  # Increase CPU and Memory to avoid timeout
     memory: 24G
   env:
+    << : *CIRRUS_EPHEMERAL_WORKER_TEMPLATE_ENV
     MAKEJOBS: "-j8"
     FILE_ENV: "./ci/test/00_setup_env_native_tsan.sh"
 
@@ -124,6 +133,7 @@ task:
   container:
     image: ubuntu:focal
   env:
+    << : *CIRRUS_EPHEMERAL_WORKER_TEMPLATE_ENV
     FILE_ENV: "./ci/test/00_setup_env_native_msan.sh"
 
 task:
@@ -132,6 +142,7 @@ task:
   container:
     image: ubuntu:focal
   env:
+    << : *CIRRUS_EPHEMERAL_WORKER_TEMPLATE_ENV
     FILE_ENV: "./ci/test/00_setup_env_native_asan.sh"
 
 task:
@@ -140,6 +151,7 @@ task:
   container:
     image: ubuntu:focal
   env:
+    << : *CIRRUS_EPHEMERAL_WORKER_TEMPLATE_ENV
     FILE_ENV: "./ci/test/00_setup_env_native_fuzz.sh"
 
 task:
@@ -148,6 +160,7 @@ task:
   container:
     image: ubuntu:focal
   env:
+    << : *CIRRUS_EPHEMERAL_WORKER_TEMPLATE_ENV
     FILE_ENV: "./ci/test/00_setup_env_native_multiprocess.sh"
 
 task:
@@ -156,6 +169,7 @@ task:
   container:
     image: ubuntu:bionic
   env:
+    << : *CIRRUS_EPHEMERAL_WORKER_TEMPLATE_ENV
     FILE_ENV: "./ci/test/00_setup_env_native_nowallet.sh"
 
 task:
@@ -164,6 +178,7 @@ task:
   container:
     image: ubuntu:focal
   env:
+    << : *CIRRUS_EPHEMERAL_WORKER_TEMPLATE_ENV
     FILE_ENV: "./ci/test/00_setup_env_mac.sh"
 
 task:
@@ -175,7 +190,7 @@ task:
     # Use latest image, but hardcode version to avoid silent upgrades (and breaks)
     image: big-sur-xcode-12.4  # https://cirrus-ci.org/guide/macOS
   env:
-    DANGER_RUN_CI_ON_HOST: "true"
+    << : *CIRRUS_EPHEMERAL_WORKER_TEMPLATE_ENV
     CI_USE_APT_INSTALL: "no"
     PACKAGE_MANAGER_INSTALL: "echo"  # Nothing to do
     FILE_ENV: "./ci/test/00_setup_env_mac_host.sh"
@@ -188,4 +203,5 @@ task:
   container:
     image: ubuntu:focal
   env:
+    << : *CIRRUS_EPHEMERAL_WORKER_TEMPLATE_ENV
     FILE_ENV: "./ci/test/00_setup_env_android.sh"