(doc) Document config via environment

This commit adds documentation for specifying vmpooler configuration via environment variables. LDAP server is corrected to LDAP host, and the capability to specify graphite prefix and port is added. Vagrant documentation is moved into its own file to reduce noise in the main readme. Lastly, docker usage is updated to reflect that you no longer bake in a configuration file, and that API and manager can be run separately from docker via its entrypoint.

docs/vagrant.md

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+A [Vagrantfile](Vagrantfile) is also included in this repository so that you dont have to run Docker on your local computer.
+To use it run:
+
+```
+vagrant up
+vagrant ssh
+docker run -p 8080:4567 -v /vagrant/vmpooler.yaml.example:/var/lib/vmpooler/vmpooler.yaml -it --rm --name pooler vmpooler
+```
+
+To run vmpooler with the example dummy provider you can replace the above docker command with this:
+
+```
+docker run -e VMPOOLER_DEBUG=true -p 8080:4567 -v /vagrant/vmpooler.yaml.dummy-example:/var/lib/vmpooler/vmpooler.yaml -e VMPOOLER_LOG='/var/log/vmpooler/vmpooler.log' -it --rm --name pooler vmpooler
+```
+
+Either variation will allow you to access the dashboard from [localhost:8080](http://localhost:8080/).
+
+### Running directly in Vagrant
+
+You can also run vmpooler directly in the Vagrant box. To do so run this:
+
+```
+vagrant up
+vagrant ssh
+cd /vagrant
+
+# Do this if using the dummy provider
+export VMPOOLER_DEBUG=true
+cp vmpooler.yaml.dummy-example vmpooler.yaml
+
+# vmpooler needs a redis server.
+sudo yum -y install redis
+sudo systemctl start redis
+
+# Optional: Choose your ruby version or use jruby
+# ruby 2.4.x is used by default
+rvm list
+rvm use jruby-9.1.7.0
+
+gem install bundler
+bundle install
+bundle exec ruby vmpooler
+```
+
+When run this way you can access vmpooler from your local computer via [localhost:4567](http://localhost:4567/).