Mount bosh-dev dir in warden containers

When I was working on the v1 services I ran into the problem of depending on warden and the service binaries (for example mongodb). Since I'm developing on osx installing warden locally is not an option. 
I found the [warden-test-infrastructure](https://github.com/cloudfoundry/warden-test-infrastructure) repo.
This would however not solve the service binary problem.

This PR is an attempt on solving the above problem by adding the ability to mount your dev directory directly inside all warden containers. This way the dependencies can be installed and compiled by bosh while you can still use your local editor.

__Usage:__
```
# Symlink your dev dir
cd bosh-lite
ln -s ~/workspace/cf-services-contrib-release/src/services/ng/mongodb bosh-dev

# Apply warden cpi patch
vagrant ssh -c /vagrant/scripts/patch_warden_cpi

# Start developing
bosh deploy
bosh ssh 
cd /bosh-dev
bundle install
rspec
```