Feat add tests

Hey.

As I plan to use this cookbook I have made some modifications : 
* I completed the README to have more informations about tests
* I corrected all rubocop errors (except LineLength & SingleSpaceBeforeFirstArg)
* I had foodcritic
* I had a simple serverspec test to check if all is fine.
* I had a .travis.yml file to launch all quick tests.

I also change the default log file location on debian (according to the `.deb` distributed by InfluxDB) and start the service automatically after installation.

What do you think of this PR ?