always remove host-only DHCP servers

A fresh install of VirtualBox automatically creates a host-only
interface (i.e., vboxnet0), with the DHCP server enabled.  This change
ensures that all DHCP servers are removed whether using Vagrant or
VirtualBox directly.

Fixes #39.
Merge pull request #92 from ericvw/dhcpserver-fix

always remove host-only DHCP servers
Ensure fluent-plugin-rewrite is installed by tightening check for gems.
(fluent-plugin-rewrite-tag-filter can be installed prior to this run.)
validate VirtualBox environment & bump min version

Introduce virtualbox_env.sh to verify that `VBoxManage` is available,
that VirtualBox meets the minimum supported version, and set the
variable VBM as a shorthand for `VBoxManage`.  If `VBoxManage` is not
available, then exit.  Otherwise, if the detected version does not meet
the minimum supported version, a warning is emitted.

Also, the minimum supported version is now bumped to be >= 4.3.x.
Merge pull request #93 from ericvw/virtualbox_env

validate VirtualBox environment & bump min version
Fix Issue #94 - VirtualBox Version Check Fails
Removing error checking; fixing immediate issue
Merge pull request #95 from cbaenziger/issue_94

Fix Issue #94 - VirtualBox Version Check Fails
provide way to peg gem versions. peg fluent-plugin-elasticsearch to 0.2.0 for now due to breakage with 0.3.0
vbox_create.sh: Do not use cache-dir unless it already exists.
vbox_create.sh: Pass args as originally intended.
Enable mod_version when using apache-mirror recipe.
Update Cirros build to 0.3.2 and change download location.
Create our binary packages before we try to set up our Chef server.
Initial commit to use Chef's upstream debs.
Tweak ordering of chef/chef-server install; allow custom cookbook packages;
patch chef-client cookbook to work out-of-the-box.
Add files forgotten in previous commit.
Get an initial chef-client run to work.
* Pass IP of server to setup_chef_server.sh and set chef-server's fqdn.
* open 443 on chef server
Lower default bootstrap VM size to 1G and add script to help run chef on
nodes.
Update upstream: ElasticSearch, Kibana, Graphite, Zabbix, Percona.