add pylint as test

.gitlab-ci.yml

+linter:
+    image: debian:stretch
+    stage: test
+    script:
+    - apt update
+    - apt install -y python3
+    - python3 -V
+    - uname -a
+    - apt install -y sqlite3 locales-all git python3-flask python3-ldap3 python3-requests python3-lxml python3-icalendar python3-mysql.connector python3-requests python3-coverage python3-pylint
+    - pylint --indent-string='\t' --indent-after-paren=1 --output-format=text *.py | tee pylint.txt
+    artifacts:
+        paths:
+        - pylint.txt
+
 unittest:
     image: debian:stretch
     stage: test