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/proxy/subcommands/ports

@@ -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"
 source "$PLUGIN_AVAILABLE_PATH/proxy/functions"
 source "$PLUGIN_AVAILABLE_PATH/config/functions"
@@ -7,7 +8,8 @@ source "$PLUGIN_AVAILABLE_PATH/config/functions"
 proxy_ports_cmd() {
   declare desc="cmd wrapper to list proxy port mappings for an app"
   local cmd="proxy:ports"
-  local APP="$2"; verify_app_name "$APP"
+  local APP="$2"
+  verify_app_name "$APP"
 
   list_app_proxy_ports "$APP"
 }