Test `drone` exists with `hash` instead of `which`.

Using `which` to test a command exists isn't considered good practice,
for more info see:

http://bit.ly/1zw8zUX
Test `drone` and `droned` exists.

Test I removed as a duplicate had the intention of testing that both
`drone` and `droned` are installed.
Add Ubuntu 14.04 LTS support to Test Kitchen.
Fix options being passed to droned.

* Fix `droned` from starting with default options (`--port=:80`) despite
  what options were set as `droned_opts` attributes.
* Add tests to make sure `droned_opts` are actually being used.
* Simplify `.kitchen.yml`, these settings are defaults / implied.
Reduce Test Kitchen OSs. Close #10.
Use Serverspec instead of Bats.
Swith from chef-solo to chef-zero.

chef-zero is becoming the recommended approach and eventually chef-solo
will be removed completely.  We may as well get in their early.

More info:  http://bit.ly/1lPTIiu
Remove unecessary string interpolation, make Foodcritic happy.
drone.conf template does not need to restart drone immediately.
Require latest Chef
Update Platforms list
Merge pull request #16 from justincampbell/serverspec

Serverspec + and droned opts fixes