Try to fix non-root CI runners

.gitlab-ci.yml

 before_script:
-  - rm -rf /usr/local/go
-  - apt-get update -qq
-  - apt-get install -y curl unzip bzip2
+  - test -f /.dockerinit && apt-get update -qq && apt-get install -y curl unzip bzip2
   - curl -O https://storage.googleapis.com/golang/go1.5.2.linux-amd64.tar.gz
   - echo 'cae87ed095e8d94a81871281d35da7829bd1234e  go1.5.2.linux-amd64.tar.gz' | shasum -c -
-  - tar -C /usr/local -xzf go1.5.2.linux-amd64.tar.gz
+  - test -f /.dockerinit && rm -rf /usr/local/go && tar -C /usr/local -xzf go1.5.2.linux-amd64.tar.gz
   - export PATH=/usr/local/go/bin:$PATH
 
 test: