[vagrant] Update Registry with #keys method.

This helper method to return the keys for the registry will give capability to eliminate some code. Example:

```ruby
keys = [] 
@subcommands.each { |k,v| keys << k }
keys.sort.each { |k| o.seperator "#{k}" }
```

Versus:

```ruby
@subcommands.keys.sort.each { |k| o.seperator "#{k}" }
```
Add unit tests for Registry#keys.
Allow defining of <install-type> and <install-type-args>
This was introduced in 1.4.1 with d26c147.

This PR sets the active hostname back to the name specified in the Vagrantfile (fqdn) and updates the unit tests.

Setting it to the short name causes loads of problems while configuring the system. I've had issues with sudoers hostname matching, Weblogic certificate generation and a few others. Even if I changed all of the Chef recipes, the fqdn is set in /etc/sysconfig/network so the active hostname will switch to the fqdn after a reboot.
Merge pull request #2792 from smoyer/redhat_hostname_patch

guests/redhat: use FQDN for hostname
core: Reintroduce `name` attribute for the `Guest`

Maintain compatibility for vagrant-vbguest plugin which uses it.
vagrant-vbguest doesn't use the caps system (to keep compatibility with
older Vagrant versions), but includes similar functionality itself.
core: Tweak host/guest capability logging

- Use downcase logger name as everywhere else
- Remove duplicate logging from the Guest
Update CHANGELOG
core: BatchAction should handle forks [GH-2756]
core: test that forking is allowed in a BatchAction
Merge pull request #2794 from tmatilai/cabability_host_name

core: reintroduce `name` attribute for the `Guest`
core: tests for Guest#name
Remove unused translations and errors thanks to @glebm
core: Remove unused error classes
Fix up translations
core: raise user-friendly errors if capabilities exception in Guest
core: more user-friendly errors for caps on guests
core: only check for box existence if not force [GH-2757]
synced_folders/nfs: automatically install NFS client if possible

If guests have the following capabilities, automatic NFS client
installation will be done:

  * nfs_client_installed - Checks if the NFS client is installed
  * nfs_client_install - Install the NFS client

Support is already in for Debian, Ubuntu, RedHat, CentOS, and Fedora
extend Virtualbox convenince methods

In the vein of #2426, I too can never remember syntax, and end up
hunting for either an exisiting Vagrantfile or starting to dig up
details.