provide option to disable apply log for innobackupex

I think it would be a good idea to let the user decide if he wants to apply the logs before the backup is stored. Disabling the apply log command reduces the required disc space considerably.

I tried to provide tests as much as possible but I don't get all of the tests running. I always get following two errors

```
[rebuy-dev@localhost backupv4]$ bundle exec rspec spec

Ruby version: ruby 1.9.3p547 (2014-05-14 revision 45962) [x86_64-linux]

Run options: include {:focus=>true}                                                                                                                                                                          
                                                                                                                                                                                                             
All examples were filtered out; ignoring {:focus=>true}
  1) Backup::Database::MySQL behaves like a class that includes Config::Helpers setting defaults allows accessors to be configured with default values                                                       
     Failure/Error: expect( klass.send(name) ).to eq expected
       
       expected: "default_prepare_backup"
            got: false
       
       (compared using ==)
     Shared Example Group: "a class that includes Config::Helpers" called from ./spec/database/mysql_spec.rb:22
     # ./spec/support/shared_examples/config_defaults.rb:31:in `block (4 levels) in <top (required)>'
     # ./spec/support/shared_examples/config_defaults.rb:29:in `each'
     # ./spec/support/shared_examples/config_defaults.rb:29:in `block (3 levels) in <top (required)>'

  2) Backup::Database::MySQL behaves like a class that includes Config::Helpers setting defaults allows defaults to be overridden                                                                            
     Failure/Error: expect( klass.send(name) ).to eq expected
       
       expected: "new_prepare_backup"
            got: false
       
       (compared using ==)
     Shared Example Group: "a class that includes Config::Helpers" called from ./spec/database/mysql_spec.rb:22
     # ./spec/support/shared_examples/config_defaults.rb:48:in `block (4 levels) in <top (required)>'
     # ./spec/support/shared_examples/config_defaults.rb:46:in `each'
     # ./spec/support/shared_examples/config_defaults.rb:46:in `block (3 levels) in <top (required)>'

 1342/1342 |===================================================================================== 100 =====================================================================================>| Time: 00:00:05 

Finished in 5.76 seconds
1342 examples, 2 failures
```

Since I'm not too much into ruby and I don't want to spend time on something you can most likely answer in a second, I'd love to hear what I've to change to get these tests running

Best regards,
Daniel