Fix Sunspot Rails not using sunspot.yml log_level setting

Sunspot will now use the configuration class to obtain the log_level
setting. The configuration class will get the log_level from sunspot.yml
settings file. If it is not present, the configuration class will use
Rails' log level setting instead.

Fixed Rails server class spec of not associating the @config instance
with the @server instance.
Merge pull request #353 from lulalala/fix_log_level

Fix Sunspot Rails not using sunspot.yml log_level setting