feature: docker advanced config

You can specify image name, user name, default command and enable/disable
cpuset. See config/worker.example.docker.yml

config/worker.example.docker.yml

@@ -0,0 +1,25 @@
+env: linux
+linux:
+  amqp:
+    host: host
+    port: port
+    username: username
+    password: password
+    virtual_host: vhost
+  vms:
+    provider: blue_box
+    count: 3
+  docker:
+    cmd:
+    username: travis
+    enable_cpuset: true
+    image_name: cip
+    default_image: cip:latest
+    private_key_path: /path/to/ssh/id_rsa
+    api:
+      host: localhost
+      port: 4234
+    memory: 4
+    expose_ports:
+  language_mappings:
+    haskell: jvm

lib/travis/worker/virtual_machine/docker.rb

@@ -46,13 +46,14 @@ def create_server(opts = {})
 
         def create_container(image_id)
           create_options = {
-            'Cmd' => ['/sbin/init'],
             'Image' => image_id,
             'Memory' => (1024 * 1024 * 1024 * (docker_config.memory || 4)),
-            'Cpuset' => cpu_set,
             'Hostname' => short_hostname,
           }
 
+          create_options['Cpuset'] = cpu_set if docker_config.enable_cpuset
+          create_options['Cmd'] = docker_config.cmd if docker_config.cmd
+
           # Allow for opting out of 'Domainname' as this results in lxc-start
           # explosions on docker 1.3.2 (and maybe others?)
           create_options['Domainname'] = domainname unless docker_config.omit_domainname
@@ -117,7 +118,7 @@ def session
           @session ||= Ssh::Session.new(name,
             :host => ssh_host,
             :port => ssh_port,
-            :username => 'travis',
+            :username => docker_config.username,
             :private_key_path => docker_config.private_key_path,
             :buffer => Travis::Worker.config.shell.buffer,
             :timeouts => Travis::Worker.config.timeouts
@@ -157,7 +158,9 @@ def fixed_ssh_host?
         end
 
         def latest_images
-          @latest_images ||= ::Docker::Image.all({}, connection).find_all { |i| image_matches?(i, /^travis:/) }
+          @latest_images ||= ::Docker::Image.all({}, connection).find_all do |i|
+             image_matches?(i, /^#{Regexp.escape(docker_config.image_name)}:/)
+          end
         end
 
         def image_for_language(lang)
@@ -174,7 +177,7 @@ def image_for_language(lang)
         end
 
         def default_image
-          latest_images.detect { |i| image_matches?(i, 'travis:ruby') }
+          latest_images.detect { |i| image_matches?(i, docker_config.default_image) }
         end
 
         def image_matches?(image, tag)