Setup python-black for auto code style fmt

Instead of having our reviewers spend time and effort commenting on
code style in changes let's make the process more automated by using
an opinionated tool like python-black.

Change-Id: Ia2724a0b38381a2ef1860c3fcd9d44bb51b8ddbb
Signed-off-by: Thanh Ha <zxiiro@gmail.com>

.pre-commit-config.yaml

@@ -1,14 +1,24 @@
 # See https://pre-commit.com for more information
 # See https://pre-commit.com/hooks.html for more hooks
 repos:
--   repo: https://github.com/pre-commit/pre-commit-hooks
-    rev: v2.0.0
+  - repo: https://github.com/python/black.git
+    rev: 19.3b0
     hooks:
-    -   id: check-added-large-files
-    -   id: end-of-file-fixer
-    -   id: flake8
+      - id: black
+        language_version: python3
+  - repo: https://github.com/pre-commit/pre-commit-hooks.git
+    rev: v2.2.3
+    hooks:
+      - id: check-added-large-files
+      - id: end-of-file-fixer
+      - id: trailing-whitespace
+  - repo: https://gitlab.com/pycqa/flake8.git
+    rev: 3.7.8
+    hooks:
+      - id: flake8
         args: ['--config=setup.cfg']
-        language: python
         types: [python]
-        additional_dependencies: [flake8>=3.6.0]
-    -   id: trailing-whitespace
+        additional_dependencies:
+          - flake8>=3.7.8
+          - flake8-black
+        language_version: python3