Run tests Docker in Docker (#261)

* Try running tests in Docker

* Spawn new container for each test

* Store test artifacts outside of mount

* When requested, build up to date image in test script

* sudo is unneccessary in containerized test env

* Skip azure test

* Backdate fixture file in JSON database

* Pin versions for azure tools

* Mount temp volume for /var/lib/docker to prevent dangling ones created by VOLUME instruction

* Fail backdating tests with message

* Add some documentation on test setup

* Cache images

* Run compose stacks with shortened default timeout

test/ssh/docker-compose.yml

@@ -8,7 +8,7 @@ services:
       - PGID=1000
       - USER_NAME=test
     volumes:
-      - ./id_rsa.pub:/config/.ssh/authorized_keys
+      - ${KEY_DIR:-.}/id_rsa.pub:/config/.ssh/authorized_keys
       - ssh_backup_data:/tmp
 
   backup:
@@ -30,7 +30,7 @@ services:
       SSH_REMOTE_PATH: /tmp
       SSH_IDENTITY_PASSPHRASE: test1234
     volumes:
-      - ./id_rsa:/root/.ssh/id_rsa
+      - ${KEY_DIR:-.}/id_rsa:/root/.ssh/id_rsa
       - app_data:/backup/app_data:ro
       - /var/run/docker.sock:/var/run/docker.sock