Speed up GitLab QA docker image builds

qa/.gitignore

+tmp/

qa/Dockerfile

@@ -8,7 +8,10 @@ RUN sed -i "s/httpredir.debian.org/ftp.us.debian.org/" /etc/apt/sources.list &&
 WORKDIR /home/qa
-COPY ./ ./
+COPY ./Gemfile* ./
+
 RUN bundle install
+COPY ./ ./
+
 ENTRYPOINT ["bin/test"]

qa/Gemfile.lock

+GEM
+  remote: https://rubygems.org/
+  specs:
+    addressable (2.5.0)
+      public_suffix (~> 2.0, >= 2.0.2)
+    capybara (2.12.1)
+      addressable
+      mime-types (>= 1.16)
+      nokogiri (>= 1.3.3)
+      rack (>= 1.0.0)
+      rack-test (>= 0.5.4)
+      xpath (~> 2.0)
+    capybara-screenshot (1.0.14)
+      capybara (>= 1.0, < 3)
+      launchy
+    capybara-webkit (1.12.0)
+      capybara (>= 2.3.0, < 2.13.0)
+      json
+    diff-lcs (1.3)
+    json (2.0.3)
+    launchy (2.4.3)
+      addressable (~> 2.3)
+    mime-types (3.1)
+      mime-types-data (~> 3.2015)
+    mime-types-data (3.2016.0521)
+    mini_portile2 (2.1.0)
+    nokogiri (1.7.0.1)
+      mini_portile2 (~> 2.1.0)
+    public_suffix (2.0.5)
+    rack (2.0.1)
+    rack-test (0.6.3)
+      rack (>= 1.0)
+    rake (12.0.0)
+    rspec (3.5.0)
+      rspec-core (~> 3.5.0)
+      rspec-expectations (~> 3.5.0)
+      rspec-mocks (~> 3.5.0)
+    rspec-core (3.5.4)
+      rspec-support (~> 3.5.0)
+    rspec-expectations (3.5.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.5.0)
+    rspec-mocks (3.5.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.5.0)
+    rspec-support (3.5.0)
+    xpath (2.0.0)
+      nokogiri (~> 1.3)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  capybara (~> 2.12.1)
+  capybara-screenshot (~> 1.0.14)
+  capybara-webkit (~> 1.12.0)
+  rake (~> 12.0.0)
+  rspec (~> 3.5)
+
+BUNDLED WITH
+   1.14.6