Allow HotRod server to be passed a cache manager class to be used instead of DefaultCacheManager

The cache manager class used by HotRod server is not pluggable. org.infinispan.server.core.Main always uses DefaultCacheManager.
Allow passing in the name of a user supplied class implementing EmbeddedCacheManager through some mean (eg a param).

I implemented this functionality already (see the attachement, look for the addition of -f param), so I hope something like this makes it into 5.0.0