CI: non consistent behaviour of branch checkout FTW

.gitlab-ci.yml

@@ -5,7 +5,6 @@ variables:
   MYSQL_ALLOW_EMPTY_PASSWORD: "yes"
 
 before_script:
-  - git checkout -b master
   - apt-get -yqq update
   - apt-get -yqq install build-essential libtool gcc-4.8 g++-4.8 make cmake openssl clang-3.5
   - apt-get -yqq install libssl-dev libmysqlclient-dev libmysql++-dev libreadline6-dev zlib1g-dev libbz2-dev libzmq3-dev