start populating stager pool when cloud controller starts

Change-Id: If4e7280effb87c9e0aecaa6f9f15fd1458230490
Remove token_endpoint from /info
Update README.md

After speaking with Kowshik, we're updating it to mention both NATS and REST calls.
Make README better.
Access all git dependencies using https

git:// URIs can be problematic as the port used by the git protocol
(9418) is often blocked for outbound connections by a firewall. The
Gemfile was using a mixture of git:// and https:// URIs for its
Git-based dependencies. This commit makes them all use https.
Use https:// rather than git:// for submodules

To avoid problems with the git protocol's port being blocked by a
firewall, use https URIs for submodules
Make symmetric_secret an optional config property.

The token validation logic in uaa_util.rb decides whether
to use symmetric or asymmetric key validation base on whether
this property is set. Without this change the CC won't start
unless it is set, hence it won't work with a UAA which is
configured to use an RSA key signature.
fixed typo when download staged app without nginx
use client_id when user_id is missing from token
Allow finding stacks by name
Correct Gemfile.lock
Fix integration test.

- Polled the startup of CCNG for quicker startup instead of unnecessary sleep
- Coped with NATS not killing itself properly
update response header content-type

  the previous type is default value, 'text/html'
correct typo
A service doesn't have a crypted password
add 'extra' attribute to services

This commit deals with the db model
[finishes #46132627] CCNG accepts 'extra' field in service offering
Fix test description to match reality
[fixes #46132627] Service #extra field is text not string
add a 'to_many spaces' relationship to domain