Fix docker-compose file (#1560)

* Make config path configurable

Add environment variable FULCIO_CONFIG to allow providing an alternate
configuration file rather than overwriting the default one. If a testing
environment overwrote the git-committed config/config.jsn, it would
pollute the repository checkout and be difficult to reuse on subsequent
test runs.

Signed-off-by: Colleen Murphy <colleenmurphy@google.com>

* Add persistent volume for mysql

The ctfe_init container uses a persistent volume to store the tree head
ID among other things from previous runs. However, the mysql container
is not guaranteed to reuse the same data directory when it is destroyed
and recreated, so it may come up empty. When this happens, but the CT
log is configured for an existing tree, then signing objects will fail
with a Not Found error. This change adds a persistent volume to the
docker-compose file for mysql so that the database can live on and be
consistent with the CT log's configuration.

Signed-off-by: Colleen Murphy <colleenmurphy@google.com>

---------

Signed-off-by: Colleen Murphy <colleenmurphy@google.com>

docker-compose.yml

@@ -37,7 +37,7 @@ services:
       - "${FULCIO_METRICS_PORT:-2112}:2112"
     volumes:
       - ~/.config/gcloud:/root/.config/gcloud/:z # for GCP authentication
-      - ./config/config.jsn:/etc/fulcio-config/config.json:z
+      - ${FULCIO_CONFIG:-./config/config.jsn}:/etc/fulcio-config/config.json:z
     healthcheck:
       test: ["CMD", "curl", "-f", "http://localhost:5555/healthz"]
       interval: 10s
@@ -109,6 +109,8 @@ services:
       timeout: 3s
       retries: 3
       start_period: 10s
+    volumes:
+      - mysql:/var/lib/mysql
   trillian-log-server:
     image: gcr.io/trillian-opensource-ci/log_server
     command: [
@@ -141,3 +143,4 @@ services:
       - mysql
 volumes:
   ctfeConfig: {}
+  mysql: {}