Introducing usage of pre-commit

The main goal is to use oslo.cache to design pre-commit for oslo.* and
then spread its use widely on oslo's world.

pre-commit will be used to:
- trailing whitespace [2].
- Replaces or checks mixed line ending (mixed-line-ending) [2].
- Forbid files which have a UTF-8 byte-order
  marker (check-byte-order-marker) [2].
- Checks that non-binary executables have a proper
  shebang (check-executables-have-shebangs) [2].
- Check for files that contain merge conflict
  strings (check-merge-conflict) [2].
- Check for debugger imports and py37+ breakpoint()
  calls in python source (debug-statements) [2].
- Attempts to load all yaml files to verify syntax (check-yaml) [2].
- replace tabs by space (4 by default)(remove-tabs) [3].
- Run flake8 checks (flake8) (local)

[1] https://specs.openstack.org/openstack/oslo-specs/specs/policy/contributing.html
[2] https://github.com/pre-commit/pre-commit-hooks
[3] https://github.com/Lucas-C/pre-commit-hooks

Change-Id: I9170cc31b91f8f25d66ff1b8537c55aced672785
Signed-off-by: Moisés Guimarães de Medeiros <moguimar@redhat.com>

.pre-commit-config.yaml

@@ -0,0 +1,35 @@
+---
+default_language_version:
+  # force all unspecified python hooks to run python3
+  python: python3
+repos:
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v3.1.0
+    hooks:
+      - id: trailing-whitespace
+      # Replaces or checks mixed line ending
+      - id: mixed-line-ending
+        args: ['--fix', 'lf']
+        exclude: '.*\.(svg)$'
+      # Forbid files which have a UTF-8 byte-order marker
+      - id: check-byte-order-marker
+      # Checks that non-binary executables have a proper shebang
+      - id: check-executables-have-shebangs
+      # Check for files that contain merge conflict strings.
+      - id: check-merge-conflict
+      # Check for debugger imports and py37+ breakpoint()
+      # calls in python source
+      - id: debug-statements
+      - id: check-yaml
+        files: .*\.(yaml|yml)$
+  - repo: https://github.com/Lucas-C/pre-commit-hooks
+    rev: v1.1.7
+    hooks:
+      - id: remove-tabs
+        exclude: '.*\.(svg)$'
+  - repo: https://gitlab.com/pycqa/flake8
+    rev: 3.8.3
+    hooks:
+      - id: flake8
+        additional_dependencies:
+          - hacking>=3.0.1,<3.1.0

tox.ini

@@ -28,6 +28,12 @@ commands =
   # Run security linter
   bandit -r oslo_cache -x tests -n5
 
+[testenv:pre-commit]
+deps =
+  pre-commit
+commands =
+  pre-commit run --from-ref HEAD^ --to-ref HEAD
+
 [testenv:venv]
 commands = {posargs}