Merge branch 'gitlab-build' into 'master'

Add a build pipeline for linux binaries.

See merge request !1

.gitlab-ci.yml

+image: docker:latest
+
+# When using dind, it's wise to use the overlayfs driver for
+# improved performance.
+variables:
+  DOCKER_DRIVER: overlay
+
+services:
+- docker:dind
+
+before_script:
+- docker info
+
+build-linux:
+  stage: build
+  script: 
+  - docker build -f Dockerfile_build_ubuntu64 -t influxdb-relay-builder:latest .
+  - docker run -v $(pwd):/root/go/src/github.com/influxdata/influxdb-relay influxdb-relay-builder --package --platform linux
+  artifacts:
+    paths:
+    - build/