pre-commit hook added + minor fixes

## pre-commit
pre-commit added to check

- `bash` files with bashate see #1109
- `yaml` files with yamlint see #1108
- `docker` files with hadolint see #1100

# hadolint

version of the linter added as a variable in the `Makefile`

.pre-commit-config.yaml

+---
+repos:
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v3.1.0
+    hooks:
+      #- id: flake8
+      - id: check-yaml
+        files: .*\.(yaml|yml)$
+  - repo: https://github.com/adrienverge/yamllint.git
+    rev: v1.23.0
+    hooks:
+      - id: yamllint
+        files: \.(yaml|yml)$
+        exclude: ^.travis
+  - repo: https://github.com/openstack-dev/bashate.git
+    rev: 2.0.0
+    hooks:
+      - id: bashate
+  - repo: local
+    hooks:
+      - id: hadolint
+        name: Hadolint linter
+        description: Runs Hadolint to check for Dockerfile best practices
+        language: system
+        types:
+          - dockerfile
+        entry: make lint-all

Makefile

@@ -26,6 +26,7 @@ ALL_IMAGES:=$(ALL_STACKS)
 
 # Linter
 HADOLINT="${HOME}/hadolint"
+HADOLINT_VERSION="v1.18.0"
 
 help:
 # http://marmelab.com/blog/2016/02/29/auto-documented-makefile.html
@@ -88,7 +89,7 @@ lint-build-test-all: $(foreach I,$(ALL_IMAGES),lint/$(I) arch_patch/$(I) build/$
 
 lint-install: ## install hadolint
 	@echo "Installing hadolint at $(HADOLINT) ..."
-	@curl -sL -o $(HADOLINT) "https://github.com/hadolint/hadolint/releases/download/v1.18.0/hadolint-$(shell uname -s)-$(shell uname -m)"
+	@curl -sL -o $(HADOLINT) "https://github.com/hadolint/hadolint/releases/download/$(HADOLINT_VERSION)/hadolint-$(shell uname -s)-$(shell uname -m)"
 	@chmod 700 $(HADOLINT)
 	@echo "Installation done!"
 	@$(HADOLINT) --version	

requirements-dev.txt

 docker
+pre-commit
 pytest
 recommonmark==0.5.0
 requests
@@ -6,4 +7,3 @@ sphinx>=1.6
 sphinx-intl
 tabulate
 transifex-client
-