Use best practices from http://www.foodcritic.io

[olivierlemasle]

Before the "corrections":

$ foodcritic -X spec/ .
FC003: Check whether you are running with chef server before using server-specific features: ./libraries/api_keys.rb:39
FC017: LWRP does not notify when updated: ./providers/api_keys.rb:40
FC017: LWRP does not notify when updated: ./providers/setup_management.rb:22
FC023: Prefer conditional attributes: ./libraries/system_template.rb:37
FC023: Prefer conditional attributes: ./recipes/management_server.rb:32
FC048: Prefer Mixlib::ShellOut: ./providers/system_template.rb:56
FC059: LWRP provider does not declare use_inline_resources: ./providers/api_keys.rb:1
FC059: LWRP provider does not declare use_inline_resources: ./providers/global_setting.rb:1
FC059: LWRP provider does not declare use_inline_resources: ./providers/setup_database.rb:1
FC059: LWRP provider does not declare use_inline_resources: ./providers/setup_management.rb:1
FC059: LWRP provider does not declare use_inline_resources: ./providers/system_template.rb:1
FC064: Ensure issues_url is set in metadata: ./metadata.rb:1
FC065: Ensure source_url is set in metadata: ./metadata.rb:1

Details of each rule can be found on http://www.foodcritic.io/.

[pdion891]

@olivierlemasle Thanks for this PR!