Fix bug with nil file resource for logfile.

This bug was introduced because Chef now checks that file resource
names are not nil.

See: https://github.com/opscode/chef/commit/b4c8facbf495423950345937ab4a8d6d8792ad16#diff-777c3a72344547b365dc6149ec4ebaffR111

This was the error encountered:

```
================================================================================
Error executing action `run` on resource 'redisio_install[redis-servers]'
================================================================================


ArgumentError
-------------
You must supply a name when declaring a file resource


Cookbook Trace:
---------------
/tmp/kitchen/cookbooks/redisio/providers/install.rb:138:in `block (2 levels) in configure'
/tmp/kitchen/cookbooks/redisio/providers/install.rb:90:in `block in configure'
```