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/plugin/commands

@@ -1,12 +1,13 @@
 #!/usr/bin/env bash
 [[ " help plugin:help " == *" $1 "* ]] || exit "$DOKKU_NOT_IMPLEMENTED_EXIT"
-set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
+set -eo pipefail
+[[ $DOKKU_TRACE ]] && set -x
 
 case "$1" in
   help | plugin:help)
-    help_content_func () {
+    help_content_func() {
       declare desc="return plugin plugin help content"
-      cat<<help_content
+      cat <<help_content
     plugin:list, Print active plugins
     plugin:install [--core|git-url [--committish tag|branch|commit|--name custom-plugin-name]], Optionally download git-url (with custom tag/committish) & run install trigger for active plugins (or only core ones)
     plugin:install-dependencies [--core], Run install-dependencies trigger for active plugins (or only core ones)
@@ -17,15 +18,15 @@ case "$1" in
 help_content
     }
 
-    if [[ $1 = "plugin:help" ]] ; then
-        echo -e 'Usage: dokku plugin[:COMMAND]'
-        echo ''
-        echo 'View installed plugins and manage community plugins.'
-        echo ''
-        echo 'Additional commands:'
-        help_content_func | sort | column -c2 -t -s,
+    if [[ $1 == "plugin:help" ]]; then
+      echo -e 'Usage: dokku plugin[:COMMAND]'
+      echo ''
+      echo 'View installed plugins and manage community plugins.'
+      echo ''
+      echo 'Additional commands:'
+      help_content_func | sort | column -c2 -t -s,
     else
-        help_content_func
+      help_content_func
     fi
     ;;
 
@@ -34,5 +35,3 @@ help_content
     ;;
 
 esac
-
-