add test for debian buster and fix linter

.gitlab-ci.yml

@@ -7,12 +7,12 @@ linter:
   - 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 pylint3
-    - pylint3 --indent-string='\t' --indent-after-paren=1 --output-format=text *.py | tee pylint.txt
+  - pylint3 --indent-string='\t' --indent-after-paren=1 --max-line-length=140 --output-format=text *.py | tee pylint.txt
   artifacts:
       paths:
       - pylint.txt
 
-unittest:
+unittest: &unittest
   image: debian:stretch
   stage: test
   script:
@@ -31,6 +31,10 @@ unittest:
       - .coverage
       - report.txt
 
+unittest_buster:
+  <<: *unittest
+  image: debian:buster
+
 livetest:
   image: debian:stretch
   stage: test