Merge branch 'pipeline-emails' into 'master'

Add a new pipeline email service

## What does this MR do?

Add a new pipeline email service

## What are the relevant issue numbers?

Closes #3976 

## Remaining tasks

* [x] Preserve `·` and ` `
* [x] Use XHTML 1.0
* [ ] Use the same layout (`app/views/layouts/notify.html.haml`)
* [ ] Digest or not (assets or public)
* [x] A similar email for succeeded pipeline
* [x] Plain text versions for both emails

## Screenshots (if relevant)

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6019#note_16594345

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [x] `PipelinesEmailService`
  - [x] `SendPipelineNotificationService`

See merge request !6019

3 files changed, 49 insertions, 0 deletions

diff --git a/lib/gitlab/ci/trace_reader.rb b/lib/gitlab/ci/trace_reader.rb
new file mode 100644
index 00000000000..37e51536e8f
--- /dev/null
+++ b/lib/gitlab/ci/trace_reader.rb
@@ -0,0 +1,49 @@
+module Gitlab
+  module Ci
+    # This was inspired from: http://stackoverflow.com/a/10219411/1520132
+    class TraceReader
+      BUFFER_SIZE = 4096
+
+      attr_accessor :path, :buffer_size
+
+      def initialize(new_path, buffer_size: BUFFER_SIZE)
+        self.path = new_path
+        self.buffer_size = Integer(buffer_size)
+      end
+
+      def read(last_lines: nil)
+        if last_lines
+          read_last_lines(last_lines)
+        else
+          File.read(path)
+        end
+      end
+
+      def read_last_lines(max_lines)
+        File.open(path) do |file|
+          chunks = []
+          pos = lines = 0
+          max = file.size
+
+          # We want an extra line to make sure fist line has full contents
+          while lines <= max_lines && pos < max
+            pos += buffer_size
+
+            buf = if pos <= max
+                    file.seek(-pos, IO::SEEK_END)
+                    file.read(buffer_size)
+                  else # Reached the head, read only left
+                    file.seek(0)
+                    file.read(buffer_size - (pos - max))
+                  end
+
+            lines += buf.count("\n")
+            chunks.unshift(buf)
+          end
+
+          chunks.join.lines.last(max_lines).join
+        end
+      end
+    end
+  end
+end
diff --git a/lib/tasks/.gitkeep b/lib/tasks/.gitkeep
deleted file mode 100644
index e69de29bb2d..00000000000
--- a/lib/tasks/.gitkeep
+++ /dev/null
diff --git a/lib/tasks/ci/.gitkeep b/lib/tasks/ci/.gitkeep
deleted file mode 100644
index e69de29bb2d..00000000000
--- a/lib/tasks/ci/.gitkeep
+++ /dev/null