tests: run mvdan/shfmt on test runs

While I do not agree with _every_ style change, this will force Dokku to have consistent formatting across all shell scripts, which is arguably a Good Thing™.

The command used to reprocess everything is:

```shell
shfmt -l -bn -ci -i 2 -w .
```

plugins/ps/subcommands/default

@@ -1,5 +1,6 @@
 #!/usr/bin/env bash
-set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
+set -eo pipefail
+[[ $DOKKU_TRACE ]] && set -x
 source "$PLUGIN_CORE_AVAILABLE_PATH/common/functions"
 
 ps_main_cmd() {
@@ -9,7 +10,8 @@ ps_main_cmd() {
 
   [[ -z $2 ]] && dokku_log_fail "Please specify an app to run the command on"
 
-  local APP="$2"; verify_app_name "$APP"
+  local APP="$2"
+  verify_app_name "$APP"
   ! (is_deployed "$APP") && dokku_log_warn "App $APP has not been deployed" && exit 0
 
   local DOKKU_APP_RUNNING_CONTAINER_IDS=$(get_app_running_container_ids "$APP")