Create rolling releases using the Gitlab API. (#171)

* Create rolling releases using the Gitlab API.

This commit builds rolling releases of Container images using the latest commit
on master branch if the pipeline passed for it. The script which gets the
references is still un-tested and should be tested.

The latest commit hashes are passed as arguments to the Dockerfile, which is
then used by PIP to install the specific version of the dependency.

get_latest_ref.py

@@ -0,0 +1,38 @@
+#! /usr/bin/env python
+import os
+import sys
+import gitlab
+
+
+def usage():
+    print("{} <project_name> <project_branch>")
+
+
+def main():
+    if 2 > len(sys.argv) > 3:
+        usage()
+
+    project_name = sys.argv[1]
+    if len(sys.argv) > 2:
+        branch_name = sys.argv[2]
+    else:
+        branch_name = 'master'
+
+    gl_token = os.getenv('GITLAB_TOKEN')
+    if gl_token is None:
+        print('GITLAB_TOKEN not set!')
+        exit(1)
+    gl = gitlab.Gitlab('https://gitlab.com/', gl_token)
+
+    project = gl.projects.get(project_name)
+    branch = project.branches.get(branch_name)
+    top_commit = project.commits.get(branch.commit['short_id'])
+
+    if top_commit.last_pipeline['status'] == 'success':
+        print(top_commit.short_id)
+    else:
+        exit(1)
+
+
+if __name__ == '__main__':
+    main()