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/certs/subcommands/remove

@@ -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"
 
 certs_remove_cmd() {
@@ -7,7 +8,8 @@ certs_remove_cmd() {
   local cmd="certs:remove"
   [[ -z $2 ]] && dokku_log_fail "Please specify an app to run the command on"
   verify_app_name "$2"
-  local APP="$2"; local APP_SSL_PATH="$DOKKU_ROOT/$APP/tls"
+  local APP="$2"
+  local APP_SSL_PATH="$DOKKU_ROOT/$APP/tls"
 
   if [[ -d "$APP_SSL_PATH" ]]; then
     dokku_log_info1 "Removing SSL endpoint from $APP"