Switch to Postgres when running tests and turn off the fsync setting (#13678)

* Run all tests fasts in postgres

* Moving postgres config to a file

* Addressing PR review comments

* Testing against mysql in the CI to keep things less changed

* Revert "Testing against mysql in the CI to keep things less changed"

This reverts commit fc940c111db269a821c54e005d76df87cb70e031.

* Fixing a test broken in postgres but working in mysql

* Fixing some tests

* Fixing some config tests with postgres

* Fixing the rest of config tests

* Fixing govet error

* Fixing search tests for postgres

build/docker-compose.common.yml

@@ -20,6 +20,9 @@ services:
       POSTGRES_USER: mmuser
       POSTGRES_PASSWORD: mostest
       POSTGRES_DB: mattermost_test
+    command: postgres -c 'config_file=/etc/postgresql/postgresql.conf'
+    volumes:
+     - "./docker/postgres.conf:/etc/postgresql/postgresql.conf"
   minio:
     image: "minio/minio:RELEASE.2019-10-11T00-38-09Z"
     command: "server /data"