Add proper build integration for CodePipeline

- Now we have proper branch information (used by Coveralls) when builds
  are started via CodePiline.
    - In order to use this integration, `SOURCEVARIABLES_BRANCH_NAME`
      MUST be set to `#{SourceVariables.BranchName}`.
- Add EventBridge rule template to trigger CodePipeline on tag pushes
  (instead of the default, which is on branch pushes).
    - Note that, regardless of triggering on tag push (format `v*`),
      CodePipeline will not use this tag as source reference. It'll use
      the HEAD of branch name configured on the source stage instead.

See: thii/aws-codebuild-extras#3

.codepipeline/buildspec-tests.yml

@@ -53,10 +53,13 @@ phases:
       - coverage xml
   post_build:
     commands:
-      # Workaround for `CODEBUILD_SOURCE_VERSION` in batch builds
+      # Workarounds for `CODEBUILD_SOURCE_VERSION` in CodePipeline or batch builds
+      # If using CodePipeline, per convention, `SOURCEVARIABLES_BRANCH_NAME` MUST be properly set.
       # See: https://github.com/thii/aws-codebuild-extras/issues/3
       - |
-        if [ ! -z "$CODEBUILD_BATCH_BUILD_IDENTIFIER" ]; then
+        if [ ! -z "$SOURCEVARIABLES_BRANCH_NAME" ]; then
+          export CODEBUILD_SOURCE_VERSION=/refs/heads/$SOURCEVARIABLES_BRANCH_NAME
+        elif [ ! -z "$CODEBUILD_BATCH_BUILD_IDENTIFIER" ]; then
           build_id=$(aws codebuild batch-get-builds --ids $CODEBUILD_BUILD_ID \
                   --query "builds[0].buildBatchArn" --output text)
           source_version=$(aws codebuild batch-get-build-batches \

extras/codepipeline-tuning/eventbridge-codepipeline-template.json

@@ -0,0 +1,12 @@
+{
+  "source": ["aws.codecommit"],
+  "detail-type": ["CodeCommit Repository State Change"],
+  "resources": ["arn:aws:codecommit:us-east-1:{AWS_ACCOUNT}:{REPOSITORY]"],
+  "detail": {
+    "event": ["referenceCreated", "referenceUpdated"],
+    "referenceType": ["tag"],
+    "referenceName": [{
+      "prefix": "v"
+    }]
+  }
+}