Handling redis connection problems in cache implementation

Hi there, I'm not sure how many people use this plugin anymore but in case it's useful we've made some changes to the caching implementation that might be generally useful.

In general, in a caching situation when failing to connect to redis we just want to have the cache not return a value, or fail to set a cached value. We don't want it to throw an exception and cause a 500 error. So this set of changes reports connection problems but generally suppresses them. Any suggestions or feedback appreciated!