Add chefspec matcher for logrotate_app definition

- assertion without a custom matcher

```ruby
it "should create appropriate log rotate config for foobar log" do 
    expect(runner).to create_template("/etc/logrotate.d/foobar").with(                                                        
      cookbook: "logrotate",                                                                                                                 
      variables: { frequency: "daily",                                                                                                       
                   rotate: 30,
                   create: "644 root adm",                                                                                                   
                   path: ["/var/log/foobar.log"], 
                   postrotate: []                                                                                                            
      })  

````
- assertion with the new custom matcher

```ruby
it "should create appropriate log rotate config for foobar log" do
    expect(runner).to enable_logrotate_app("foobar").with(
      cookbook: "logrotate",
      path: "/var/log/foobar.log",
      frequency: "daily",  
      rotate: 30,
      create: "644 root adm"
      )
    end
````