Add support for virtualenv and pip

Change-Id: I09647b254f6d7c17bbbbba6351c5e9abe0081bbd

cloud_controller/staging/common.rb

@@ -26,6 +26,8 @@
 require File.expand_path('../gemfile_task', __FILE__)
 require File.expand_path('../gem_cache', __FILE__)
 
+require File.expand_path('../virtualenv_support', __FILE__)
+require File.expand_path('../pip_support', __FILE__)
 
 # TODO - Separate the common staging helper methods from the 'StagingPlugin' base class, for more clarity.
 # Staging plugins (at least the ones written in Ruby) are expected to subclass this. See ruby/sinatra for a simple example.

cloud_controller/staging/pip_support.rb

@@ -0,0 +1,13 @@
+module PipSupport
+
+  REQUIREMENTS_FILE = 'requirements.txt'
+
+  def uses_pip?
+    File.exists?(File.join(source_directory, REQUIREMENTS_FILE))
+  end
+
+  def install_requirements
+    "../env/bin/pip install -r #{REQUIREMENTS_FILE}"
+  end
+
+end

cloud_controller/staging/virtualenv_support.rb

@@ -0,0 +1,10 @@
+module VirtualenvSupport
+
+  def setup_virtualenv
+    cmds = []
+    cmds << "virtualenv --no-site-packages env"
+    cmds << "env/bin/pip install gunicorn"
+    cmds.join("\n")
+  end
+
+end

cloud_controller/staging/wsgi/plugin.rb

@@ -1,4 +1,7 @@
 class WsgiPlugin < StagingPlugin
+  include VirtualenvSupport
+  include PipSupport
+
   def framework
     'wsgi'
   end
@@ -13,13 +16,20 @@ def stage_application
   end
 
   def start_command
-    "gunicorn -c ../gunicorn.config app:app"
+    cmds = []
+    if uses_pip?
+      cmds << install_requirements
+    end
+    cmds << "../env/bin/gunicorn -c ../gunicorn.config app:app"
+    cmds.join("\n")
   end
 
   private
   def startup_script
     vars = environment_hash
-    generate_startup_script(vars)
+    generate_startup_script(vars) do
+      setup_virtualenv
+    end
   end
 
   def create_gunicorn_config