friendlier error handling for log file permission errors

[colinsurprenant]

Errno::ENOENT: No such file or directory - 
              mkdir at org/jruby/RubyDir.java:581
           fu_mkdir at /home/jenko/.rvm/rubies/jruby-1.7.0.preview1/lib/ruby/1.9/fileutils.rb:247
            mkdir_p at /home/jenko/.rvm/rubies/jruby-1.7.0.preview1/lib/ruby/1.9/fileutils.rb:221
       reverse_each at org/jruby/RubyArray.java:1691
            mkdir_p at /home/jenko/.rvm/rubies/jruby-1.7.0.preview1/lib/ruby/1.9/fileutils.rb:219
               each at org/jruby/RubyArray.java:1611
            mkdir_p at /home/jenko/.rvm/rubies/jruby-1.7.0.preview1/lib/ruby/1.9/fileutils.rb:205
  setup_file_logger at /home/jenko/.rvm/gems/jruby-1.7.0.preview1@barebones/gems/raad-0.5.0/lib/raad/logger.rb:42
              setup at /home/jenko/.rvm/gems/jruby-1.7.0.preview1@barebones/gems/raad-0.5.0/lib/raad/logger.rb:17
      start_service at /home/jenko/.rvm/gems/jruby-1.7.0.preview1@barebones/gems/raad-0.5.0/lib/raad/runner.rb:91
                run at /home/jenko/.rvm/gems/jruby-1.7.0.preview1@barebones/gems/raad-0.5.0/lib/raad/runner.rb:80
               run! at /home/jenko/.rvm/gems/jruby-1.7.0.preview1@barebones/gems/raad-0.5.0/lib/raad/bootstrap.rb:44
               Raad at /home/jenko/.rvm/gems/jruby-1.7.0.preview1@barebones/gems/raad-0.5.0/lib/raad/bootstrap.rb:63