Refactor Config#mkdir and #mkAppDataDir

This is a pure refactoring that renames and inlines variables to tighten
up and make more consistent the implementation of these two methods. It
is done in preparation for a subsequent substantive change that fixes a
bug.

common/src/main/java/bisq/common/config/Config.java

@@ -797,14 +797,13 @@ private static File tempUserDataDir() {
      * nothing if the directory already exists.
      * @return the given directory, now guaranteed to exist
      */
-    private static File mkAppDataDir(File appDataDir) {
-        Path path = appDataDir.toPath();
+    private static File mkAppDataDir(File dir) {
         try {
-            Files.createDirectories(path);
+            Files.createDirectories(dir.toPath());
         } catch (IOException ex) {
-            throw new UncheckedIOException(format("Application data directory '%s' could not be created", path), ex);
+            throw new UncheckedIOException(format("Application data directory '%s' could not be created", dir), ex);
         }
-        return appDataDir;
+        return dir;
     }
 
     /**
@@ -815,11 +814,10 @@ private static File mkAppDataDir(File appDataDir) {
     private static File mkdir(File parent, String child) {
         File dir = new File(parent, child);
         if (!dir.exists()) {
-            Path path = dir.toPath();
             try {
-                Files.createDirectory(path);
+                Files.createDirectory(dir.toPath());
             } catch (IOException ex) {
-                throw new UncheckedIOException(format("Directory '%s' could not be created", path), ex);
+                throw new UncheckedIOException(format("Directory '%s' could not be created", dir), ex);
             }
         }
         return dir;